No towing power, any one have this problem?

[mtdave2]

a few updates.. first off, i cant read a vacuum gauge. its 13, not 16. the cover is scratchy, and...well doesn’t matter..lol..

2nd, we took it out for a drive and rapped the hell out of the motor. there were a few times that around 4900 rpm, you could feel a bit of a surge in power. enough to make us both look at each other and ask , did you feel that?

so more indications of a cam problem.

first time i took the camper out since i put the rebuilt carb, new coil, cap,rotor, wires, and plugs on.. there was noticeable difference in power, but wasn’t THE problem. still a dog, no torque.

this week, ill take he timing chain cover off and look to see that its not off a tooth. if it isn’t, out comes the cam.

i hope i solve this soon, i don’t have time for this shyt

[Mertz]

I know this is an old thread but I am having the same problem and I would like to know if you solved your problem and what it was. My motor has the stock cam and MSD ignition and I have done all the tests you have. All the suggestions were good and I checked out each one on my truck except the fuel filter. The pressure guage shows about 5.5 psi at idle which is right for the qjet.

[mtdave2]

To add to this. I had the motor stroked by one of the best engine shops in south Texas. So, I have a 383, new rebuilt qjet ,I swapped out the torque converter for a supper wazoo TC I high torque towing converter….results? About the same. I through my hands up and had not touched it for a year.

I finally have the truck up in Chicago now (I moved). I am starting to play with things again. First step was to fix all my crap wiring that I did. There was a few issues, but nothing that would effect power.

I took the carb off and made sure all the bolts and screws were tight, I did find several that were a bit more loose that they should have been. There is a chance they were loose enough to cause a vacuum leak. The truck did seem to idle better when I was done.

Next step is to take it to a garage and put it on the computer. I want to verify everything is tuned and runner right.

The jerkbag the rebuilt my trany, I have no confidence in now. I am thinking about just ordering a new trany from monster, just for piece of mind, and to take the trany out of the equation. It may be an emotional thing, but I feel the power loss is in the trany, or the rear end. Now the rear end, I will be addressing that as well. I am wanting a posi but finding parts for this rear end may be rough…will see what happens.

[swamp rat]

Subscribed, not the kinda soap opera anybody wants to read or experiance but definantly a thread to learn from.

[mtdave2]

amen on the soap opera.

[Vintage Windmills]

does the driveshaft turn freely when in nuetral? Seems like the rear end should be pretty easy to rule out if this is the case. Also, if it was a driveline issue you'd probably feel the truck decelerate when you lifted off the gas.

I am really curious to see what the problem is when you find it. Good luck!

[capev86]

ummm.....bad fuel filter may flow enough gas at idle but when the engine demands more fuel it gets starved and stumbles. maybe you should change it anyway if it is not new (or there is any chance something from the tank got sucked up and plugged it.

[Mertz]

That light just came on for me too. Enough fuel to sound good at idle or light cruise but not enough when power braking or pulling.

Let's hope that is my the problem. It will be a lot more fun to drive.

[alsohim]

Man u got too much gear. i bet u have .308 or .356's. If .308 put a ring and pinion in. with these old trucks the cheapest HP was gears. My C20 Custom Camper has .411 from the factory. Bad news is my truck needs and overdrive lol.

JMHO
Kaleb

[DANTIP]

Twenty years ago I bought a near perfect 1967 GTO with an H.O. 400 because the previous owner was fed up with the lack-luster performance (it had A/C and 3.07 gears). My dad (guru mechanic) rode in the car one time and told me my secondaries were not opening. I was 100% convinced he was wrong because the throttle was opening properly and the TH400 was downshifting (which I mistook for secondaries opening) but was later thrilled to learn that the secondary controls on the Quadrajet 4MV were not allowing the secondaries to open. I replaced the choke pull-off and adjusted the spring on the top secondary blade and literally found about 100 HP. My throttle linkage was opening the lower blades, but the top blade was not opening. The secondaries on a Q-Jet respond to load and cannot be easily tested. Let us know if any breakthroughs are made!

Merry Christmas!!

[Stubbs67]

throw an edelbrock on it, woke up my 307 in my old 68

[mtdave2]

after i got all the bolts and screws of my carb tight, and replaced a few of the vaccum plugs, the truck ran smoother. my vaccum jumped from 15 to 17.

because i have a vortec intake, my stock remote choke didnt work, so i put on an electric conversion. i had to make a bracket for that too, and it just doesnt work well. i have been screwing around with it. i may just give up and go to manual one! it is getting close i think..

so that said, i am thinking my power loss is a mix of many things. vaccum leaks, choke issue, and after reading posts, my secondarys may not be opening, or maybe not all the way...ill look into that next.

my throtle return spring was a tad light, so it wasnt bringing the main butterfly all the way closed, so my idle was always a tad high. i fixed that.

now, if i floor it at a stop, the motor stubmles....never had that happen before! tomorrow ill check the timing..it probably needs bumped up now. also i guess this is a sign of my secondarys now not opening...?

anyway, i think im making progess..

[Stubbs67]

how much compression does it make?

maybe the dynamic compression ratio isn't high enough (cam related)

also make sure the carb functions correctly. I had lots of issues with my quadrajet, my friend's dad rebuilt it and he was a really good mechanic. replaced it and man it was a different truck.

[j_cst_10]

I tried to read through the posts but could find if you set the timing. What total timing do you have and at what rpm does it come in? Also, what is your air fuel ratio? The engine is only as good as it's tune.

I added 2 degrees of timing and took out 2 jet sizes on a chassis dyno and gained 40 rwhp on my 383 monte carlo ss.

[mr48chev]

At first I thought you were just flat expecting too much out of the truck as my 71 3/4 ton with the 350 slows down pretty good when pulling my sailboat over the pass to Puget Sound but that is a 5000 foot+ high pass. Lots of miles at 45 in second gear with the turbo 350 most of the time to keep the rpm up in the working range.

On my truck headers helped a lot as I had pretty restricted exhaust from what I could tell.
Also have you checked the fuel line from the tank to the carb for kinks, twists and or smashed spots. All too often someone will put a twist or kink in the line when tightening up a fitting that causes a huge restriction and almost shuts off the fuel flow when you really need it for power.

[Mertz]

I don't know about mtdave but my carb is built and tested by Cliff Ruggles and works fine. I have had another qjet on it that I built with the help of the LC-1 A/F meter and I have had a Edelbrock on it. The qjet far out performs the Edelbrock. I know my secondaries are opening by sound.

As for the gears we both should be turning the tires with the 4.10s and should be limited in top speed but we are both able to hit 85 plus with no problem. Mine still has pedal left. I just bought a digital tach I will be installing to check rpms. Right now I drive via the vacuum gauge. I try to keep the vacuum as high as possible. I am at 19 at idle (800 rpm) when the engine is warm. Very steady needle.

I will be checking the fuel lines. I just put in a new sending unit so I have already checked that end of it. There is a line in the front of the truck that was plugged by the former owner. It leaked a few times when I filled it and it was hot. I thought it might be a vent so I unplugged it and drove it to the gas station filled the truck and drove to the store. When I parked it it was pouring gas out of the tube. Needles to say that I replugged it. I also have a chrome gas cap that the gasket goes bad on so I made a gasket out of single ply roofing material. I could be that I don't have enough ventilation for the tank but I don't remember ever hearing a sucking sound when I open the cap at the gas station.

I can still get premium gas with no ethanol when I am on vacation and pulling the trailer. It does run better with no ethanol.

I have tried a lot of different timing settings and might go just a little more retarded to 10 initial.

I am sure I don't have any vacuum leaks. I am also running with no choke and it starts fine even when it is 13 degrees out. To me that is an indication that engine is running fine.

[j_cst_10]

A good rule of thumb for a small block chevy is 34-36 degrees of total timing. This number is taken with a dial back timing light at lets say 5,000rpm with the vacuum advance canister unplugged and your carb temporarily plugged. The reason for the high rpm is to account for any mechanical advance. The higher rpm ensures that you will see your total amount of timing.

Also with a timing light and tachometer record at what rpm you start seeing your timing change and plot a curve with graph paper or microsoft excel. The timing curve can help you get information from distributor manufacturers for the right amount of timing and where you want it to come in at. With street strip applications you want it to all come in by 3,000rpm, but towing you might want it to come in later to avoid detonation.

Once you have set the timing, try driving it around before plugging the vacuum advance in. I have seen faulty canisters that create vacuum leaks or pull way to much timing at part throttle.

Don't underestimate the proper amount of timing. It can wake up or kill and engine if it is not set right. Even a couple of degrees makes a difference.

Also, check valve lash. If you set this incorrectly it can limit valve lift and rpm and change the characteristics of your cam.

[Mertz]

I haven't plotted the curve but I have set it to 34 and 36 degrees all in at 2800. I have been higher and lower. I have seen on HorsepowerTV where a couple of degrees makes a big difference. I don't have any pinging even when towing. I might try going to 10 initial because I read on line that the reversions are less likely at around 10. I might try putting in as much as possible and backing off 3 degrees when it pings.

My vacuum advance puts in a little more than I want so I dropped the initial to keep total around 51. I do use a dial back timing light and I have checked TDC but will do it again.

I am going out to the shop now and check fuel in lines and might even do some checks for TDC.

Merry Christmas to all.

[Mertz]

I had some time before going out today so I went into the shop with the sun glistening on the snow.

I pulled the fuel filter and found it full of fine rust particles. So I spliced in a solid line and will relocate the new filter later.

I checked the timing and I was at 14 initial giving me 37 all in at 2500.

I decreased the timing and it did not sound right so I bumped it until is sounded strong and I took a reading. I was at 19 initial with good throttle response and a good sound. I checked the total with vacuum and I was at 60. I decided to back it off a little but keep it up where it had good throttle response. I backed it down to 18 with 41 all in at 2500 and a total with vacuum at 58. I am running ported vacuum but with the previous 2 carbs I ran manifold which gave me more timing at idle. It ran better with this carb on ported but now that I have the timing up I might go back to manifold and see which is better. I am wondering if this engine just likes that much timing or my damper has slipped. I would like to reduce that amount of vacuum advance so it is around 51 all in. I don't have an adjustable canister. I will check with MSD and see what they can recommend. BTW I got my idle vacuum back up to 18 which is probably about as high as I can get it.

To bad I won't be able to do any test drives since I can't get the truck out of the shop.

Merry Christmas

[j_cst_10]

The adjustable canisters are pretty cheap. 41 degrees is a lot of timing but if you have older, less efficient cylinder heads it is possible to need that.

The best advice I can give about tuning is locating a cheap chassis dyno to go to. I have one near me and the guy is reasonable. I won't do any more tuning without it, it is worth the money to dial it in. You can see things on a dyno that you won't be able to see.

This is the before and after on a chassis dyno with my 383 monte carlo. Notice how the curves smooth out and also look at the change in scale (RWHP). My initial ballpark tuning was close, all I did was take the air/fuel ratio from 12.0:1 to 12.5:1 and added 2 degrees of total timing. Best money I spent hp per dollar.

before


after

[Mertz]

I spent a little time on the truck today and installed a new fuel filter and put some dielectric grease on the spark plug boots. I have done any more with the timing and will wait and see what it does on the road.

I did cut my old fuel filter in half just to see how bad it was. It was so packed with rust that feels like fine sand that the only fuel getting through was at the top of the filter. I put on a clear filter this time up near the carb so I can keep track of it. The old one was on the truck when I bought it. It should have been one of the first things I changed. I changed all the fluids but failed to change this one filter and it really has caused me some problems but I gain a wealth of knowledge trying to figure out why I did't have any power.

I will be resetting the carb with the LC-1 this spring and checking with the local dyno shop. Your new curves look really smooth and I bet it runs much better. I did do a short power brake test but did not floor it for fear of going through the garage wall and it has noticeably more power as it actually stood up when I punched it.

I bet I can break them loose now.

[oldgold70c10]

If your having choke issues with the q-jet & it is affecting the secondaries, do yourself a favor and step up to a later q-jet that uses the choke mounted on the carb. These can be easily converted to electric choke and perform much more reliably. Best years are 76-80.

[dwragon]

I know you have had alot of advice, but here some things that may help. you havent said exactly what type of RV you have, just that it is Chevy based. If it has the typical chevy van nose, the rear end depends on if its a dually or not (ei 373/411 gears). If it is the RV built on a box truck/ 1 ton dually frame, it could have 411/456/513/530 gears. These gears fool alot of people into thinking its not running right cause its not running fast. A mule is still a mule no matter how much you flog it.

One other thing I did not see mentioned is if it has a passenger choke heat rizer flapper. If these get stuck closed or part closed, they will make it act like your describing. If completely closed, they will cause an engine to overheat and crack a head on the passenger side.

[mtdave2]

dwragon i was just looking at that flap yesterday! i was hoping it was half closed, but it was open... great point though, im sure that thing has caused a few ppl lots of problem.

i wont have time to play with my truck for a few weeks, but i did make progess this week. finding and fixing the vaccume leaks and a timing bump gave her more power as well as making it start better. just a quick bump is all it needs now.

i am really wondering if my 2nds are opening all the way..first thing ill look into. i also have to sort out the stumble when i floor it, could be the same issue, but????

as far as the rv. we both have c20s PULLING campers. also, may people have said that they think i am just wanting too much out of the truck. i am getting to the point i wana strangle them! hahah I KNOW what these trucks can do, and mine is not doing it. now its just the why.....

[Mertz]

Mtdave: I can help with the stumble. The things to check are the pump shot and the spring tension on the secondaries. Usually the spring is set from 3/4 turn to 7/8 turn from touch. I always adjust this with the carb off because it is hard to loosen the allen screw and hold the screw at the same time. You need to hold the screw or it will fly and you might break the spring. Never go over one full turn. On the pump shot make sure your rod is in the hole closest to the pump. It will give you a better shot. You need to look into the carb and make sure you get a good shot. You can call Cliff Ruggles at Cliff's Performance and he will help you get it right. I have spent a lot of time with him via emails and he has helped a lot. Also some qjets are set not to open all the way. Check and make sure yours does. Also make sure that your lockout is not keeping the secondaries from opening. They won't open if the choke is on. It has to be completely open to release the lock out. If the lockout is bypassed and the choke is not completely open it will get too much air and bog. Once you get the qjet tuned you won't ever have to adjust it again and it should perform like you have an EFI just make sure your fuel filter isn't plugged LOL.

dwragon: I pull a 6000lb trailer and have the same 4.10 rear end as mtdave. I have headers so there is no exhaust flap. The carb I am using was a very good carb according to Cliff. He set it up with an APT adjustment like the later carbs.