Rebuilt Monojet, dies when stopping moderately hard

[Superdrag67]

As the title says I just rebuilt the monojet and also replaced the float. It runs and idles great, much better than before. The problem is that now it dies anytime that I come to a stop and have to push on the breaks harder than normal. Even normally I can kinda feel it miss a little like the engine wants to die. I adjusted all the specs according to the little sheet in the rebuild kit. My guess is the float needs to be set higher but I'm not sure. And I'd prefer not to tear it apart more than once (if possible) to fix the problem so I thought I'd ask here first to see if anyone has any ideas. Thanks in advance!

[Wrenchbender Ret]

2 ideas. The power brake unit may have a bad diaphragm.
The float level may be too high.

[PanelDeland]

Or a vacuum leak.

[mechanicalman]

Originally Posted by Superdrag67

As the title says I just rebuilt the monojet and also replaced the float. It runs and idles great, much better than before. The problem is that now it dies anytime that I come to a stop and have to push on the breaks harder than normal. Even normally I can kinda feel it miss a little like the engine wants to die. I adjusted all the specs according to the little sheet in the rebuild kit. My guess is the float needs to be set higher but I'm not sure. And I'd prefer not to tear it apart more than once (if possible) to fix the problem so I thought I'd ask here first to see if anyone has any ideas. Thanks in advance!

What they said. Also, while sitting still idling, try pushing on the brakes moderately and hard to see if it has any effect on idle, and if it causes any noise like air leaking (vacuum). It should make no difference whether the truck is moving or not for the vacuum booster to lose vacuum if it's leaking. It can leak from the diaphragm like already stated or the "power piston" in the center of the diaphragm.

That being said, if your float is set correctly then there is no reason why YOUR float needs to be higher when everyone else's do not. I doubt a foam float would be bad enough right away to sink, but if the new one is brass then maybe it has a leak.

Critical question: Did you rebuild the carb and replace the float for this reason or did it NOT have this particular problem before you rebuilt it?

Ask yourself, did the problem "create itself"? (Part or unit failure).

OR

Did I create it, and what did I do to create it?

[Superdrag67]

Thanks for the replies everyone! Forgot to mention that I do no have power brakes, so that wouldn't be the issue. I guess I could still have a vacuum leak elsewhere though? One of the vacuum caps didn't fit real tight but I don't think that would be the issue.

I didn't have this problem before rebuilding the carb. I rebuilt the carb because one day when parking the truck I had a bunch of gas flooding out of the carb. I don't know if that was the first time or just the first time I caught it. Anyways I figured rather than try and take apart and clean a crusty old carb I would just rebuild it. I'm glad I did because there just plenty of junk floating around inside it and it honestly just idle and run much smoother now. It is a new brass float.

I'll double check float level and see what it's set at.

[mechanicalman]

Originally Posted by Superdrag67

Thanks for the replies everyone! Forgot to mention that I do no have power brakes, so that wouldn't be the issue. I guess I could still have a vacuum leak elsewhere though? One of the vacuum caps didn't fit real tight but I don't think that would be the issue.

I didn't have this problem before rebuilding the carb. I rebuilt the carb because one day when parking the truck I had a bunch of gas flooding out of the carb. I don't know if that was the first time or just the first time I caught it. Anyways I figured rather than try and take apart and clean a crusty old carb I would just rebuild it. I'm glad I did because there just plenty of junk floating around inside it and it honestly just idle and run much smoother now. It is a new brass float.

I'll double check float level and see what it's set at.

If the float level is good (not too low) then take the float out and see if it has any gas in it.

[Superdrag67]

Bumping this back up top to see if anyone else has any ideas. Finally had some free time today and I messed around with the thing for 4 hours today with no changes. So frustrating!

I lost track of how many times I had the carb apart. Right now it's set right about factory specs for the float level. Still dies when coming to a stop. The float does not have any gas in it. I adjusted the float probably 6-8+ times (up and down) and no matter where the level was, the problem did not go away. Though how quickly it would die and how hard I had to hit the brakes to cause it to die did seem to change some as I adjusted.

Also the truck fires right back up after it dies, doesn't need to crank or anything. Also it will stay running if I use one foot to give it some gas while breaking so I don't see how it's anything other than a fuel issue.

Metering Rod adjustment seems to be right on. Messing with the Idle mixture screw also had no affect.

I threw away all the old stuff but I did change the jet to the new one that was in the rebuild kit. I didn't look to see if they were identical, could this be a problem? Also I'm adjusting the carb based on specs provided in the spec sheet with the rebuild kit. I'm just using the one for the year/engine of my truck. Or is it really more carb specific? What if the carbs been changed?

Can't find any vacuum leaks. Vacuum advance seems to be working right though my timing mark on the harmonic balancer shows on the opposite side of the timing tab when I try to check timing. Not sure if the HB was replaced or the rubber slipped or what.

I'm going crazy here!

[mechanicalman]

Originally Posted by Superdrag67

Bumping this back up top to see if anyone else has any ideas. Finally had some free time today and I messed around with the thing for 4 hours today with no changes. So frustrating!

I lost track of how many times I had the carb apart. Right now it's set right about factory specs for the float level. Still dies when coming to a stop. The float does not have any gas in it. I adjusted the float probably 6-8+ times (up and down) and no matter where the level was, the problem did not go away. Though how quickly it would die and how hard I had to hit the brakes to cause it to die did seem to change some as I adjusted.

Also the truck fires right back up after it dies, doesn't need to crank or anything. Also it will stay running if I use one foot to give it some gas while breaking so I don't see how it's anything other than a fuel issue.

Metering Rod adjustment seems to be right on. Messing with the Idle mixture screw also had no affect.

I threw away all the old stuff but I did change the jet to the new one that was in the rebuild kit. I didn't look to see if they were identical, could this be a problem? Also I'm adjusting the carb based on specs provided in the spec sheet with the rebuild kit. I'm just using the one for the year/engine of my truck. Or is it really more carb specific? What if the carbs been changed?

Can't find any vacuum leaks. Vacuum advance seems to be working right though my timing mark on the harmonic balancer shows on the opposite side of the timing tab when I try to check timing. Not sure if the HB was replaced or the rubber slipped or what.

I'm going crazy here!

Disclaimer: Don't try this on a crowded street LOL
Question: If you were to give it just a little throttle while you are braking, will it still die?

I'm thinking if a little throttle keeps it from dying, you might have a fuel pump not keeping up at idle.

I used to have a Ford 6 cyl that would die turning left, rebuilt the carb, found no problem, did not fix it. Then, put in a new brass float but made no difference. Found out it was a problem with the factory style float design, installed a new Ford updated design float (different configuration) (not brass, composite foam) and it fixed it.

I recommend you get a GM float, maybe a similar problem to what I had. Also, did the kit come with a clip to hold the needle valve to the float itself to prevent sticking?

Not sure you can still get a new GM float for that carb. If you can't get one, try a new composite one.

Composite (foam) floats actually work better. Lighter, float better. Got a bad rap as some early ones would get fuel-logged but newer ones are good.

[Superdrag67]

If I give it some gas while braking it will stay running. The fuel pump looks newer but that doesn't mean it's working right I guess. Just weird that this started after I rebuilt the carb.

I can order the composite float so maybe I'll try that and see if it helps.

The kit did come with the little clip but I dropped it and then couldn't find it.

[mechanicalman]

Originally Posted by Superdrag67

If I give it some gas while braking it will stay running. The fuel pump looks newer but that doesn't mean it's working right I guess. Just weird that this started after I rebuilt the carb.

I can order the composite float so maybe I'll try that and see if it helps.

The kit did come with the little clip but I dropped it and then couldn't find it.

The clip is probably the only problem. Go to a carb shop they will probably give you one. If not, just get a new needle and seat provided it comes with the clip, and I think they all do.

Do the clip first, IMO.

[Superdrag67]

I didn't worry about getting another clip because I read in a few places that it didn't really matter.

How would not having the clip affect gas flow during breaking? Seems like it would be most important under heavy acceleration to make sure the needle lifted back up and didn't stick. There wasn't one in there when I tore it all apart either.

I'll see if I can track one down.

[mechanicalman]

Originally Posted by Superdrag67

I didn't worry about getting another clip because I read in a few places that it didn't really matter.

How would not having the clip affect gas flow during breaking? Seems like it would be most important under heavy acceleration to make sure the needle lifted back up and didn't stick. There wasn't one in there when I tore it all apart either.

I'll see if I can track one down.

If it started only after you rebuilt the carb then it's obviously something you did to the carb so I'm not so hot on the clip being the root cause, seeing how it didn't have one before; although if you take the carb apart you should replace it.

Did you install the brass float? Did it have a foam one in it before?

They don't put clips in because it doesn't matter. Higher pressure like on high performance cars usually have higher fuel pressure like 7 lbs or so and they tend to keep the needle pushed up and stock style fuel pumps tend to run a little lower and the clip is to keep the needle from sticking.

The monojet is a side hung (transverse) float, when your float is at the top, inertia can hold it there by sideloading the float from braking and the fuel bowl can go dry. A lighter foam float would be less effected by inertial forces. What I'm reading into this is that inertial force is acting upon the float enough to hold it at the top restricting fuel flow enough to run the bowl dry, and with increased RPM the pressure of the fuel increases and is enough to push the needle up and break the float loose to allow fuel flow.

My Ford 6 cyl had a front hung (longitudinal) float and it stuck only turning left.

Don't forget, all we have to go on is what you have told us we did not see the carb apart. It's still clear as mud. I cannot say if a different pump or float will fix it.

If you put the Old float back in it, or the Equivalent, Logic says it will probably work if everything else is Equal to before.

[Superdrag67]

It's too bad I threw the old float away otherwise I'd swap it back in to try out. Ugh. What you are saying does sound plausible. I thought the brass were supposed to be better and it was half the price so I figured I'd go with that.

It could be coincidence but I agree it must be something with the carb. The float and possibly some adjustments were the only things that changed. Well I guess the Jet got changed too.

I can't imagine the Jet being too small and having a similar issue where it would run dry from inertia and kill the truck. Is that possible? Initially when I rebuilt the carb I didn't change the metering rod adjustment, just wanted to leave it where it was at and see how it ran. After messing with the float and having it apart I did change it to what the spec sheet listed which was a lower than where it was set. It didn't make the problem worse however.

If I'm going to order a new float I might just get a new needle with clip to try it out also.

Thanks for all the help.

[mechanicalman]

Originally Posted by Superdrag67

It's too bad I threw the old float away otherwise I'd swap it back in to try out. Ugh. What you are saying does sound plausible. I thought the brass were supposed to be better and it was half the price so I figured I'd go with that.

It could be coincidence but I agree it must be something with the carb. The float and possibly some adjustments were the only things that changed. Well I guess the Jet got changed too.

I can't imagine the Jet being too small and having a similar issue where it would run dry from inertia and kill the truck. Is that possible? Initially when I rebuilt the carb I didn't change the metering rod adjustment, just wanted to leave it where it was at and see how it ran. After messing with the float and having it apart I did change it to what the spec sheet listed which was a lower than where it was set. It didn't make the problem worse however.

If I'm going to order a new float I might just get a new needle with clip to try it out also.

Thanks for all the help.

I cannot see the jet being the problem. Never seen a carb kit come with the jet that's in the bottom of the fuel bowl, but they always come with the needle and the needle's seat. Most of the needle's seats are slotted for wide blade screwdriver removal, and they look much like a jet.

The metering rod goes in the main jet. Sorry if you knew all that.

[mechanicalman]

Originally Posted by Superdrag67

It's too bad I threw the old float away otherwise I'd swap it back in to try out. Ugh. What you are saying does sound plausible. I thought the brass were supposed to be better and it was half the price so I figured I'd go with that.

It could be coincidence but I agree it must be something with the carb. The float and possibly some adjustments were the only things that changed. Well I guess the Jet got changed too.

I can't imagine the Jet being too small and having a similar issue where it would run dry from inertia and kill the truck. Is that possible? Initially when I rebuilt the carb I didn't change the metering rod adjustment, just wanted to leave it where it was at and see how it ran. After messing with the float and having it apart I did change it to what the spec sheet listed which was a lower than where it was set. It didn't make the problem worse however.

If I'm going to order a new float I might just get a new needle with clip to try it out also.

Thanks for all the help.

Re-reading your post. The inertia I speak of is inertia of the float itself and the weight of the float, when braking, side-loading the float causing it to stay up even when the fuel level goes down. That's why when you stop applying inertia (brakes) it starts and runs again.

Foam floats are lighter as I have experienced them than brass.

Check to see if the end of the float is possibly rubbing against the side of the float bowl maybe near the bolt boss towards the end of the float, then when you get your new float make sure it's not.

[Superdrag67]

This rebuild kit did come with the jet. I can't imagine that's the problem either though.

I'll get some parts and report back. Might be a few weeks before I get the time to mess with it again though.

[Superdrag67]

Bumping this thing again.

Got back around to working on it a bit.
In the last week I replaced the PCV valve and vacuum hose to it. Removed the air horn and cleaned out the idle circuit a dozen+ times with carb cleaner and compressed air to make sure nothing was stuck in there, had the throttle shaft rebushed and put in a new foam float. Found one on ebay that was only $12 instead of the $30 I was looking at. I was having a hard time spending spending $30 when I felt like I was just throwing it away so I kept putting it off.

Anyways, nothing made any difference. At times I think it's a little better and then the next time I test it out it's just the same. Checked and double checked float settings and metering rod adjustments and even played with them to no avail.

After a decent amount of internet searching I found one thread where a person was having identical problems to mine with their monojet and they finally just replaced the carb. Of course that's no help to me. Everything else I've found was either vacuum related or float settings or something like that.

I'm losing my mind here and I don't know what else to do with it.

It doesn't matter what speed i'm going, whether it's 5 mph or 30mph, if I hit the brakes hard it dies instantly but will start right back up with no problem.

Also sprayed carb cleaner around multiple times looking for a vacuum leak and can't find anything.

[mechanicalman]

Originally Posted by Superdrag67

Removed the air horn and cleaned out the idle circuit a dozen+ times with carb cleaner and compressed air to make sure nothing was stuck in there, had the throttle shaft rebushed and put in a new foam float. Found one on ebay that was only $12 instead of the $30 I was looking at. I was having a hard time spending spending $30 when I felt like I was just throwing it away so I kept putting it off.

Anyways, nothing made any difference. At times I think it's a little better and then the next time I test it out it's just the same. Checked and double checked float settings and metering rod adjustments and even played with them to no avail.

It doesn't matter what speed i'm going, whether it's 5 mph or 30mph, if I hit the brakes hard it dies instantly but will start right back up with no problem.

"if I hit the brakes hard it dies instantly"

I'm starting to think it's not the carb. If you can accelerate without running out of fuel, you ought to be able to apply the brakes without it dying immediately. It should take some time to deplete the fuel bowl; longer than dying immediately upon braking.

Do you know anyone who has a truck or vehicle that takes the same type carb that you could swap carbs with to see if the problem follows the carb?

You are going to have to start thinking outside the box. Get a set of long extension leads to go from the engine bay into the cab.

How loose is the distributor shaft? Put the extension leads on a dwell meter inside the cab and watch the meter while braking and see if the dwell changes or goes away.

Using the extension leads with a volt meter or 12V check light, check to see if you lose voltage to the hot side of the coil when you put on the brakes.

Swap coils.

That's about all there is, at least for what I know.

[barmanvarn]

Rebuilt my first carb last week (another Monojet). Fires up fine. Can't drive it yet because, no brakes.

Subbed, in case I run into this at some point.

Hope you figure it out. Good luck!

[truckdude239]

Auto or manual? Wonder if the torque converter not letting going

[Superdrag67]

It's a manual.

Mechanicalman - Appreciate all the input in this thread. I had ruled out ignition issues because if I pull the choke on the carb or keep my foot on the gas while braking it won't die. Those two things make me think it had to be fuel related. Otherwise I would dig into the ignition side of things. To me that says that somehow it's starving for fuel under hard braking or at least that's what I think but I'm far from an expert. Yet it dies so fast I have a hard time seeing how it could be fuel either. I'm just totally baffled and frustrated.

There really is so very little to a monojet I just don't see what could be causing it. My only other thought would be to take the carb back off and take it to someone who can soak the whole thing for me. Maybe the carb cleaner and compressed air isn't getting a chunk out somewhere.

I don't know anyone with a similar truck. Thinking about finding another monojet locally and swapping it out to see what happens.

[Superdrag67]

One other question. I had ruled it out as being an issue based up what little I could find on the net but at this point I'll look at anything.

My monojet doesn't have a idle vent on top of the air horn like I see in a lot of monojets. However I noticed that not all monojets have them. Is it there on particular monojets or used in certain cases? Mine does have the hole but there is just a plug there that looks factory. Same as the plugs i've seen in other pics that I assumed were stock carbs.

Is that something that is used with the automatic choke or something? I honestly have no idea what it's supposed to do. I'll get some pics if needed.

Not my carb, just a pic from the web. That big slotted screw on top is the idle vent. Mine is plugged.

[barmanvarn]

Mine had an automatic choke and also has a plug where the vent hole is. I noticed this when doing my rebuild last week.

I had asked my Dad if it was like this from the factory, but he wasn't sure. I'm guessing it was.

I doubt that helps, but figured I'd tell you what I knew.

[Superdrag67]

Just thought I would update the thread in case someone has similar issues in the future. Happened to pick up a gallon can of carb cleaner from a friend so I pulled the carb off, disassembled and let it soak for 2 days. Flushed off and blew out with compressed air and put it back together.

Problem solved! I guess something was stuck in one of the passages.

Pretty happy about this. Unfortunately life happens and I put the truck up for sale so probably won't enjoy it too much longer.
I've learned tons from this forum, so much good info on here.

Look at that happy face!

[mechanicalman]

[QUOTE=Superdrag67;7080183]Just thought I would update the thread in case someone has similar issues in the future. Happened to pick up a gallon can of carb cleaner from a friend so I pulled the carb off, disassembled and let it soak for 2 days. Flushed off and blew out with compressed air and put it back together.

Problem solved! I guess something was stuck in one of the passages.

Well you showed some amazing "sticktoit-tiveness"

You saved her, too bad you have to her go.

I'm sure you know that carb Inside and Out!

Here, here, to the MONOJET KING!