Rochester Monojet Help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Sgt.Booya · 06-09-2006, 01:57 PM

Hi Guys, I just got my truck and I'll be the first to admit I'm a bit of a "tool" when it comes to mechanical expertise, however, I'm usually brave enough to try

I'm planning on replacing my inline six at some point but for now I want to get it running smooth. Hoping you guys could give me a hand?

The Problem:
It's REAL hard to get going.
If I just feather on the gas I can get it to catch after about 15 starting attempts. If I let it idle for about 5 mins I can gradually apply more gas very slowly and raise the RPMs. Too much gas and it stalls out. After its up to tempature I can drive it.

The Equipment:
1970 Chev Rochester MonoJet for an inline 6. 250cc. Casting number# 7040021

What I think is wrong:
I think it's the choke. I've never seen a carb like this before it doesn't have a choke on it? I think it's detached? (See pic)

.

The Solution: (and here's where I need your help)
* I can't seem to find a replacement choke (rebuild kits yes, chokes, no). Anybody point me in the right direct here?
* Is there another carb I could buy that would work on the inline 6 with the choke incorporated? Remember the engine is going likely in the next 12 months [It would have to be low $$$ solution] and there looks to be a fairly elaborate mechanism to operate the specific carb on there now. Looks like anything else (newer) would require from creative fabrication.

* Has anybody ever hooked up a manuel choke under the dash for this carb?

I'd appreciate your input and advice of what you feel might be the easiest way to fix this.....Thanks

Ps: New points and wires....I think its definately an air/fuel thing.

texnician01 · 06-09-2006, 02:25 PM

What your arrow is pointing at is not the choke that is an idle solenoid. The choke will be right under the threaded rod for the air cleaner. It looks like it is there in the pics but I can't tell for sure. the shaft closes to the top will be the choke shaft. the small linkage rod on the back of that shaft should go to the throttle butterfly and the one on the front of that shaft should go to the Intake manifold and have a bi-metal spring under a small cover. The spring is all that controls the choke. There are a few other carbs that will fit that engine without too much trouble. My old 292 had a Model 1940 Holley on it. worked well. About any single barrel rochester will fit but the linkage is the hard part to adapt. You may be able to put a cable choke on the one you have but it may involve fabricating a bracket for the cable housing and getting one of the little brass endpieces to activate the choke. Sorry if that wasn't much help. I don't have any of these carbs around anymore or I could maybe help with some parts.

Nathan

shelby987 · 06-09-2006, 03:03 PM

Pic. isn't loading for me, but my truck had that same carb, and it had a cable choke mounted under the dash. It appeared to be one of those off the shelf k-mart jobs. The only bracket you will need will be one to mount it to one of the bolts that holds the valve cover down.....I would bet you could get a piece of angle iron from Home depot and just use some creative bending.....I had the exact same problem though, with or without the choke....I think the carb might need a complete rebuild.......

If however, you are just looking for an easy way to start it....i found that if I tapped the gas when turning the key (continued tapping, about 1/3 of the way down), I could get it to start....once it kicks DON'T stop tapping the pedal, begin to increase the depth of the tapping until you are a llittle less than half way to the floor....then stop tapping, holding your foot half way down, this will allow you to get to an idle of about 2k or so (never had a tach when I had this problem), after about 2 or 3 mins. of high idle, you can let your foot off and it will idle fine.....if you had a stick shift like mine, you could just slide it into gear, but with an automatic it might just stall you out again.

Hope this helps......if you just want it to run and start, this should work, but this is by no means a final solution.

Sgt.Booya · 06-09-2006, 03:48 PM

Shelby987, I'm sitting here laughing my a$$ off.

The way you described the sequence of events you have to go through to get it running is perfect. That is EXACTLY my problem. I just never thought anybody could desribe it so well.

Still at a bit of a loss though. Since the idle solenoid definately isn't the choke.

(I warned you, I'm a mechanically challenged)

Guess I'm down to 1) Rebuild 2) Bolt on something different and figure out the linkage 3) Try a manual choke cable

Interested to see how others would handle it? Opinions?

PanelDeland · 06-09-2006, 04:08 PM

I had pretty much the same problem with mine.It would start on the manual choke but would stutter and balk when trying to take off(manual tranny).It was also sometimes hard to start.I found the problem when I changed the points and plugs.When I timed it,the timing wasn't changing when the throttle was pushed.The vacuum advance was bad.I replaced it and the engine starts better and there's very little to no stutter when taking off.To check just remove the vacuumn hose and plug it.If the advance is bad there will probably be little change.Vacuum is high at idle so it will affect your idle if the vacuum advance is bad.

texnician01 · 06-09-2006, 04:15 PM

I think I would go find a good book with exploded views for that carb or look on the net, rebuild it, and put on a manual choke, shouldn't be too bad. Wish I still had mine, you could bot it on, hook up the choke, throttle rod and one hose, throw out the rest of that crap you have on that poor motor. lol! Of course you always have the option of the offy 4 bbl intake and header...

Good luck
Nathan

texnician01 · 06-09-2006, 04:16 PM

try a book like this

http://cgi.ebay.com/ebaymotors/Book-...spagenameZWDVW

Nathan

shelby987 · 06-09-2006, 05:01 PM

As stated, I had the same problem and I had a working manual choke, the choke would help to keep it running once I got it past the sputter, sputter, stall point, but it took at LEAST a min or two of warm up before the choke made a difference, and there was still only a small "sweet spot"
I have actually since swapped my carb for the 4bbl and headers....and the engine just sounds MEAN! My points and vaccum advance are fine, totally a carb problem. IIRC, the motor craft 350 2bbl carb is a bolt on???

Sgt.Booya · 06-09-2006, 10:55 PM

Humm, OK so even with the manuel choke shelby987 had the same problem, so it's probably not entirely a choke problem...and PanelDeland sharpened his up by correcting the vaccum advance.

Based on your advice here's what I plan to do:
1) Check and test the Vaccum advance. If that doesn't work, I'll........
2) Take Texnician01's advice and pull the whole Carb off, clean and rebuild it. If that's not it, I'll......
3) Bolt on a whole different Carb and figure out some new linkage.

Ps: Hey shelby987 aren't MotorCraft parts made for.......(Dare I say the "F" word on this website???) Gulp........FORDS?

Thanks guys, appreciate the insight.

Canadian72GMC · 06-10-2006, 09:43 AM

the arrows in the picture clockwise from top left are ; choke rod, choke plate and choke thermostatic coil. Make sure that on a cold engine, the choke plate is lightly closed. The choke thermostatic coil is actually a temperature sensitive bi-metal spring that puts tension on the choke rod as it cools off. You can buy these, and it is likely your problem.

ST Dog · 04-22-2009, 02:16 PM

Resurrecting an old post.

Anyone got pictures of the monojet linkages?
I think have a problem with the fast idle cam.

'68 GMC, manual choke. Story is the engine was replaced in '72 with a new engine from a Nova (dealer warranty replacement best I can tell).

The number on the carb points to a '72 carb.
I think it was modified some for the manual choke though.
The coil is still on the intake with the linkage rod, but it's not attached to the cab, and no place to attach it either. There is a rod from the rear of the choke shaft to a cam at the base which looks like a fast idle cam.

Anyway, when I close the choke it doesn't move the fast idle cam much (if at all). If I move the cam by hand, noting in the throttle linkage touches it. Looks like I need to bend a tab on the throttle linkage to set the fast idle, but until the choke moves the cam it won't help much.

68gmsee · 04-22-2009, 07:03 PM

Here's a bump for you...

I've got a Rochester monojet with manual choke on my 68 GMC. I'm not sure how much of a difference there was in the linkages between the early and later years, but I can post a pic later tonight.

Is the choke linkage and fast idle cam the only pic you need?

ST Dog · 04-22-2009, 10:20 PM

Quote:

Originally Posted by 68gmsee

Here's a bump for you...

I've got a Rochester monojet with manual choke on my 68 GMC. I'm not sure how much of a difference there was in the linkages between the early and later years, but I can post a pic later tonight.

Is the choke linkage and fast idle cam the only pic you need?

I think so, the rest seams OK. I just want to verify that everything is there, or figure out what's missing.

68gmsee · 04-22-2009, 10:44 PM

Well, the pics I took looked like crap so I'll get some with a different camera tomorrow morning.

OhNoJoe · 04-28-2009, 12:03 AM

I woulod be interested in getting a pic from the front of that carb set-up. I can't seem to figure out how the choke rod is supposed to be bent and hooked up for my 292
I got some carb pictures you may want to look at

http://s221.photobucket.com/albums/d...2pulled077.jpg

ST Dog · 04-28-2009, 09:25 AM

Quote:

Originally Posted by OhNoJoe

I woulod be interested in getting a pic from the front of that carb set-up. I can't seem to figure out how the choke rod is supposed to be bent and hooked up for my 292

I hop these help some. I don't know if the linkage has been bent over the years or not.

06-09-2006, 01:57 PM	#1
Sgt.Booya Registered User Join Date: Apr 2006 Location: Ontario, Canada Posts: 75	Rochester Monojet Help Hi Guys, I just got my truck and I'll be the first to admit I'm a bit of a "tool" when it comes to mechanical expertise, however, I'm usually brave enough to try I'm planning on replacing my inline six at some point but for now I want to get it running smooth. Hoping you guys could give me a hand? The Problem: It's REAL hard to get going. If I just feather on the gas I can get it to catch after about 15 starting attempts. If I let it idle for about 5 mins I can gradually apply more gas very slowly and raise the RPMs. Too much gas and it stalls out. After its up to tempature I can drive it. The Equipment: 1970 Chev Rochester MonoJet for an inline 6. 250cc. Casting number# 7040021 What I think is wrong: I think it's the choke. I've never seen a carb like this before it doesn't have a choke on it? I think it's detached? (See pic) . The Solution: (and here's where I need your help) * I can't seem to find a replacement choke (rebuild kits yes, chokes, no). Anybody point me in the right direct here? * Is there another carb I could buy that would work on the inline 6 with the choke incorporated? Remember the engine is going likely in the next 12 months [It would have to be low $$$ solution] and there looks to be a fairly elaborate mechanism to operate the specific carb on there now. Looks like anything else (newer) would require from creative fabrication. * Has anybody ever hooked up a manuel choke under the dash for this carb? I'd appreciate your input and advice of what you feel might be the easiest way to fix this.....Thanks Ps: New points and wires....I think its definately an air/fuel thing. __________________ If you keep and open mind you never know what might drop in. 1970 Chev C10 SWB, "250 turbo thrift"

06-09-2006, 02:25 PM	#2
texnician01 Senior Member Join Date: Mar 2002 Location: 12 Miles South of Des Moines, Iowa Posts: 359	Re: Rochester Monojet Help What your arrow is pointing at is not the choke that is an idle solenoid. The choke will be right under the threaded rod for the air cleaner. It looks like it is there in the pics but I can't tell for sure. the shaft closes to the top will be the choke shaft. the small linkage rod on the back of that shaft should go to the throttle butterfly and the one on the front of that shaft should go to the Intake manifold and have a bi-metal spring under a small cover. The spring is all that controls the choke. There are a few other carbs that will fit that engine without too much trouble. My old 292 had a Model 1940 Holley on it. worked well. About any single barrel rochester will fit but the linkage is the hard part to adapt. You may be able to put a cable choke on the one you have but it may involve fabricating a bracket for the cable housing and getting one of the little brass endpieces to activate the choke. Sorry if that wasn't much help. I don't have any of these carbs around anymore or I could maybe help with some parts. Nathan __________________ 69 C-10, 340HP 327 55 chevy 4 door 150 47 Willys CJ-2A 05 Harley Night Train 06 1200 Sportster (Wife's bike) 70 Honda CL350 OIF2 & OIF7 Veteran Nathan & Tiffany

06-09-2006, 03:03 PM	#3
shelby987 Registered User Join Date: Mar 2005 Location: Just outside Durham, NC Posts: 894	Re: Rochester Monojet Help Pic. isn't loading for me, but my truck had that same carb, and it had a cable choke mounted under the dash. It appeared to be one of those off the shelf k-mart jobs. The only bracket you will need will be one to mount it to one of the bolts that holds the valve cover down.....I would bet you could get a piece of angle iron from Home depot and just use some creative bending.....I had the exact same problem though, with or without the choke....I think the carb might need a complete rebuild....... If however, you are just looking for an easy way to start it....i found that if I tapped the gas when turning the key (continued tapping, about 1/3 of the way down), I could get it to start....once it kicks DON'T stop tapping the pedal, begin to increase the depth of the tapping until you are a llittle less than half way to the floor....then stop tapping, holding your foot half way down, this will allow you to get to an idle of about 2k or so (never had a tach when I had this problem), after about 2 or 3 mins. of high idle, you can let your foot off and it will idle fine.....if you had a stick shift like mine, you could just slide it into gear, but with an automatic it might just stall you out again. Hope this helps......if you just want it to run and start, this should work, but this is by no means a final solution. __________________ 1969 SS 350 Camaro Sold 2008 1970 3/4T K20, stock height with 33's, 250 I6, 3 on the tree, and locked front and rear 4.10's 1980 Chevy Malibu 2 dr Sold 2007 1993 Olds. Cutlass Ciera Wagon Traded 2006 2003 Saturn L200 w/5pd. D/D My list spans 5 decades with One common thread.....GM! Last edited by shelby987; 06-09-2006 at 03:04 PM.

06-09-2006, 03:48 PM	#4
Sgt.Booya Registered User Join Date: Apr 2006 Location: Ontario, Canada Posts: 75	Re: Rochester Monojet Help Shelby987, I'm sitting here laughing my a$$ off. The way you described the sequence of events you have to go through to get it running is perfect. That is EXACTLY my problem. I just never thought anybody could desribe it so well. Still at a bit of a loss though. Since the idle solenoid definately isn't the choke. (I warned you, I'm a mechanically challenged) Guess I'm down to 1) Rebuild 2) Bolt on something different and figure out the linkage 3) Try a manual choke cable Interested to see how others would handle it? Opinions? __________________ If you keep and open mind you never know what might drop in. 1970 Chev C10 SWB, "250 turbo thrift"

06-09-2006, 04:08 PM	#5
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,993	Re: Rochester Monojet Help I had pretty much the same problem with mine.It would start on the manual choke but would stutter and balk when trying to take off(manual tranny).It was also sometimes hard to start.I found the problem when I changed the points and plugs.When I timed it,the timing wasn't changing when the throttle was pushed.The vacuum advance was bad.I replaced it and the engine starts better and there's very little to no stutter when taking off.To check just remove the vacuumn hose and plug it.If the advance is bad there will probably be little change.Vacuum is high at idle so it will affect your idle if the vacuum advance is bad. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil" Last edited by PanelDeland; 06-09-2006 at 04:09 PM.

06-09-2006, 04:15 PM	#6
texnician01 Senior Member Join Date: Mar 2002 Location: 12 Miles South of Des Moines, Iowa Posts: 359	Re: Rochester Monojet Help I think I would go find a good book with exploded views for that carb or look on the net, rebuild it, and put on a manual choke, shouldn't be too bad. Wish I still had mine, you could bot it on, hook up the choke, throttle rod and one hose, throw out the rest of that crap you have on that poor motor. lol! Of course you always have the option of the offy 4 bbl intake and header... Good luck Nathan __________________ 69 C-10, 340HP 327 55 chevy 4 door 150 47 Willys CJ-2A 05 Harley Night Train 06 1200 Sportster (Wife's bike) 70 Honda CL350 OIF2 & OIF7 Veteran Nathan & Tiffany

06-09-2006, 04:16 PM	#7
texnician01 Senior Member Join Date: Mar 2002 Location: 12 Miles South of Des Moines, Iowa Posts: 359	Re: Rochester Monojet Help try a book like this http://cgi.ebay.com/ebaymotors/Book-...spagenameZWDVW Nathan __________________ 69 C-10, 340HP 327 55 chevy 4 door 150 47 Willys CJ-2A 05 Harley Night Train 06 1200 Sportster (Wife's bike) 70 Honda CL350 OIF2 & OIF7 Veteran Nathan & Tiffany

06-09-2006, 05:01 PM	#8
shelby987 Registered User Join Date: Mar 2005 Location: Just outside Durham, NC Posts: 894	Re: Rochester Monojet Help As stated, I had the same problem and I had a working manual choke, the choke would help to keep it running once I got it past the sputter, sputter, stall point, but it took at LEAST a min or two of warm up before the choke made a difference, and there was still only a small "sweet spot" I have actually since swapped my carb for the 4bbl and headers....and the engine just sounds MEAN! My points and vaccum advance are fine, totally a carb problem. IIRC, the motor craft 350 2bbl carb is a bolt on??? __________________ 1969 SS 350 Camaro Sold 2008 1970 3/4T K20, stock height with 33's, 250 I6, 3 on the tree, and locked front and rear 4.10's 1980 Chevy Malibu 2 dr Sold 2007 1993 Olds. Cutlass Ciera Wagon Traded 2006 2003 Saturn L200 w/5pd. D/D My list spans 5 decades with One common thread.....GM!

06-09-2006, 10:55 PM	#9
Sgt.Booya Registered User Join Date: Apr 2006 Location: Ontario, Canada Posts: 75	Re: Rochester Monojet Help Humm, OK so even with the manuel choke shelby987 had the same problem, so it's probably not entirely a choke problem...and PanelDeland sharpened his up by correcting the vaccum advance. Based on your advice here's what I plan to do: 1) Check and test the Vaccum advance. If that doesn't work, I'll........ 2) Take Texnician01's advice and pull the whole Carb off, clean and rebuild it. If that's not it, I'll...... 3) Bolt on a whole different Carb and figure out some new linkage. Ps: Hey shelby987 aren't MotorCraft parts made for.......(Dare I say the "F" word on this website???) Gulp........FORDS? Thanks guys, appreciate the insight. __________________ If you keep and open mind you never know what might drop in. 1970 Chev C10 SWB, "250 turbo thrift"

06-10-2006, 09:43 AM	#10
Canadian72GMC Registered User Join Date: Mar 2005 Location: north battleford, sk Posts: 30	Re: Rochester Monojet Help the arrows in the picture clockwise from top left are ; choke rod, choke plate and choke thermostatic coil. Make sure that on a cold engine, the choke plate is lightly closed. The choke thermostatic coil is actually a temperature sensitive bi-metal spring that puts tension on the choke rod as it cools off. You can buy these, and it is likely your problem. Attached Images

04-22-2009, 02:16 PM	#11
ST Dog Registered User Join Date: Feb 2009 Location: BFE Mississippi Posts: 23	Re: Rochester Monojet Help Resurrecting an old post. Anyone got pictures of the monojet linkages? I think have a problem with the fast idle cam. '68 GMC, manual choke. Story is the engine was replaced in '72 with a new engine from a Nova (dealer warranty replacement best I can tell). The number on the carb points to a '72 carb. I think it was modified some for the manual choke though. The coil is still on the intake with the linkage rod, but it's not attached to the cab, and no place to attach it either. There is a rod from the rear of the choke shaft to a cam at the base which looks like a fast idle cam. Anyway, when I close the choke it doesn't move the fast idle cam much (if at all). If I move the cam by hand, noting in the throttle linkage touches it. Looks like I need to bend a tab on the throttle linkage to set the fast idle, but until the choke moves the cam it won't help much.

04-22-2009, 07:03 PM	#12
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Rochester Monojet Help Here's a bump for you... I've got a Rochester monojet with manual choke on my 68 GMC. I'm not sure how much of a difference there was in the linkages between the early and later years, but I can post a pic later tonight. Is the choke linkage and fast idle cam the only pic you need?

04-22-2009, 10:44 PM	#14
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Rochester Monojet Help Well, the pics I took looked like crap so I'll get some with a different camera tomorrow morning.

04-28-2009, 12:03 AM	#15
OhNoJoe Registered User Join Date: May 2006 Location: Springfield Illinois Posts: 182	Re: Rochester Monojet Help I woulod be interested in getting a pic from the front of that carb set-up. I can't seem to figure out how the choke rod is supposed to be bent and hooked up for my 292 I got some carb pictures you may want to look at http://s221.photobucket.com/albums/d...2pulled077.jpg



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