Vapor lock issues.

[kevmic28]

Originally Posted by Notrodder

My thoughts: Do the test that cdowns suggested with the new pump. If it's getting gas to the carb, check that the screws and mounting bolts on the carb are tight. Turn the throttle linkage and see that everything is opening as it should so you're getting air to match the gas. Now try turning your fuel metering screws on the base of the carb in a quarter turn and see if there's any improvement, if not try one half turn out and check again. This may or may not solve your problem, but it is easy to do and worth a try.

Another thing, it was a long time ago that this happened to me so I can't remember the symptoms, but the float in my carb sank and caused some kind of aggravating problem that a new float cured. Does anybody here think that this could be kev's problem?

Where are the fuel metering screws??

[grs]

If you are going to keep the truck why don't you just rebuild the carb?

[Notrodder]

Originally Posted by kevmic28

Where are the fuel metering screws??

They are in the front of the carb down low on the base. Two of them, spring loaded. I guess some people call them idle mixture screws.

[kevmic28]

Yes I am going to keep the truck had it almost a year now. The carb is not even a year old. Honestly it shouldnt need to be rebuilt.
What is the base setting for the idle mixture screws?

[Notrodder]

Originally Posted by kevmic28

What is the base setting for the idle mixture screws?

I don't know offhand, but if you just run them in a little bit you can see if they will help with your problem.

"Idle mixture screw" can be misleading, they will affect how the truck runs beyond idle. Once you find where the truck likes them, slight changes will make a big difference. I live at sea level, but when I drive inland my truck runs better if I close each one about 1/8 turn.

[kevmic28]

Ok Ill mess with it tomorrow. Its too late tonight. I am gonna pull the carb tomorrow also and just make sure everything is clean and clear.

[68gmsee]

Don't assume that just because the carb has been rebuilt it is not the problem. I've had to return a few rebuilt ones in the past.

As Notrodder mentioned check the idle mixture screws before taking the carb apart. Be sure and carefully count the turns when adjusting them. I usually start with a base setting of 1-1/2 to 2 turns out after gently seating them all the way in.

Use a vacuum gauge if you have one and adjust for the highest vacuum you can get. This should get you close to what you need.

Couple of other things I'd check.

Take the dist cap off and using mouth suction make sure your vacuum advance is working -with no leakage. It doesn't take a lot of vacuum to move it if it's working properly.

Insure you're getting the max amount of fuel by taking the fuel line off the carb and place in a plastic container. Should get about a pint of fuel in app. 20-30 seconds or less. (be sure and disconnect the coil wire first)

[kevmic28]

yeah I checked the fuel yesterday after I put the new pump on and I am getting the proper amount of fuel, that bucket filled up quick. I was wondering about the vacuum advance also. Ill start with the metering screws in a few minutes.

[70' GMC]

I had the inline fuel filter its plastic and its like 6 or 7 bucks I can't remember now if it has went up in price. Also get sum deep sea carb cleaner it goes in the tank get 2 or 3 cans its in a red and white can. I had like sputtering issues and decided to crank the truck up and pour a whole can into the carb and it cleaned the gunk up. It just smoked up the place and it gets rid of mosquitos for me it did. And I put 2 cans in the tank and 93 octane for 2 weeks and the truck ran good. Also open the cap before you leave home and also when you leave work. I hated when it happened. That truck was ol reliable it would crank and run it was just mean on gas. I hope it will help you out.

[kevmic28]

Ok I have been messing around with the metering. Set at 1 and a half turns, no change. 1/8 turns out to 3 turns and no change. turned it in a half a turn from 1 1/2 and it starts to die.
It idles great but once I put it gear and step on the gas it bogs down again. If I floor it it hauls, but once I let off the gas say at 55mph it spits and sputters and take almost full gas pedal to stay at speed.
Kinda makes me think the secondary jets are clogged. How do the secondaries fire? via the accel pump or vacuum? Can I learn over the carb and push the throttle see the secondaries pump gas or does the engine have to be running to pump them I guess is what I am asking.
If I go back to what I originally found I had a bunch of crap from my inline filter in the carb filter. Now the principle of this filter is that a spring is behind and the filter can move based of fuel pressure, so if pressure was too high the filter will move back and the fuel will bypass the filter till the pressure is down. If that is the case then the crud could have bypassed the filter and clogged up the jets.
I think I wil go ahead and pull my carb and check the jets out to make sure they are not clogged.
Other idea I have is that maybe the cap and rotor is just bad. I may just pick up a new cap and rotor while I am in town to check them out.
I also removed the inline filter and just using the in carb filter for now. I was thinking maybe it was causing my issues, but nope its not.

[oldgold70c10]

The idle mixture screws only come into play at idle and off-idle transition. The simple way to adjust them is to turn them in until lightly seated, then back them out 4 turns, set the idle speed, and then turn the screws in equally about 1/4 turn at a time until the engine speed changes, then back them off 1/4 turn from there. It really sounds like you've got a float or primary metering problem. The secondaries only come into operation when you floor it, and how much depends on engine speed.

It is very likely that trash from the filter is clogging up the jets as you suspect, and it could also be causing problems with the float level too.

Your best bet is to rebuild the carb.

[kevmic28]

Ok added a new cap and rotor. Runs better but still not like it should.
ran the mixtures out to 4 turns and turned them on 1/4 turns and it is running better but at around 1500 rpms it stalls if I let off or gun it it returns to the normal.

[oldgold70c10]

OK, so basically you have no part throttle. Your problem is in the carb. Something has plugged up the tiny passages inside that the fuel flows through.

Rebuilding a Q-jet isn't very hard, but it might be intimidating the first time. You'll need a kit. On the driver's side of the carb there will be some numbers stamped. You'll need to write those down and take to the auto parts store to get the right kit.

[kevmic28]

Ok sounds like I am rebuilding the carb tomorrow.
One more question. I added new spark plugs just before I started having issues. They were pregapped at .035. Now from what I have been reading these might be gapped wrong. What should the gap numbers be for a 350 with a hei and no emmissions on it?

[oldgold70c10]

All my rides have HEI & I've been gapping them .060"

[kevmic28]

Ill pull them in the morning and regap them. Could having them gapped at .035 possibly be causing some of my issues?

[oldgold70c10]

Originally Posted by kevmic28

Ill pull them in the morning and regap them. Could having them gapped at .035 possibly be causing some of my issues?

I don't think it should, unless when you pull the plugs a lot of them have crud caked on them and you can't see the gap! If it idles OK and doesn't sound or feel like its missing I doubt the plugs are giving you any trouble. .035 is the gap for plugs with stock points ignition. With the HEI, you can run a wider gap. Clean your plugs and regap to .060 and try it before tearing into the carb just to see.....

[Notrodder]

I believe the correct gap is .045 for HEI ignition. You'll want to do this anyway and then you can tell us if it helps.

I know that these things can be a frustrating pain, but it builds troubleshooting skills and familiarity with our trucks systems. At least now, you have the luxury of dealing with this at home. Sometime, at the side of the road, this kind of knowledge will be of huge value. When you get it worked out, share the knowledge with the rest of us.

[kevmic28]

Yeah side of the road sucks. I a front tire blow out on my Harley blow out on me two weeks ago and I sat on the side of the road for 3 hours waiting on a tow truck. Never been so happy to be home in my life.. lol

[Notrodder]

Just today I had to remove my Q-jet and free a stuck float valve on the side of the road. I was glad that I had the tools and ability, rather than have to rely on someone else to save my...
I've only had this truck ('71 1/2 ton) for a couple of weeks and am just finding out what needs attention on it. It has had some fuel delivery problems, so your thread is of particular interest to me.

[68_chop_top]

I had this problem on a 85 Surburban. Changed fuel pumps and filters, rebuilt carb, and even dropped the tank for a cleaning. Spacers and heat shields, rubber fuel lines and back to metal with insulation around it. Nothing! Absolutely nothing I did would fix the vapor lock. Drive the truck to local gas station and fine. Drive to Dallas for the boys soccer game and on the way home, puck, strand us on the side of the road for an hour til it cools down and drive the rest of the way home. Not fun. This went on for several years and everything I did I thought I fixed it. NOPE! Finally another car and the sub went to the side of the garage. My oldest boy wanted to drive it for his first car so I thought I would fix it up. Yeah it had headers and Flows on it and sounded good but he wanted more so I suggested a cam. Sounds funny but its a kid and a suburban so why not. Swapped bumpy cam and he drove it several years with no problem. WHY?!?! I thought of something and went and miked the cam lobe for the fuel pump and there was only 0.003" of a lobe. New cam and lobe generates enough pressure to push gas under hot (high back pressure) conditions. This was my fix and I still drive that suburban today in Texas heat with no problems and 340,000 miles on the odometer. This may or may not be your problem but a worn cam will give some pressure but not enough for all conditions.
Good luck to you.

[kevmic28]

So that throws wind to putting on an electric fuel pump then. Except its a new cam. Well its suppose to be. Had a rebuilt engine installed in November.
I started looking at the plugs today. The plugs I removed were ac delco cr45ts and the new plugs I put in last week before I started having issues are r43ts. I dont know if it makes a difference but I do not believe the new plugs are for my truck. Im still researching it though.
Anybody know about these plugs.

[kevmic28]

Also could it be a timing issue?

[rollinhard]

if its running good up at higher rpms its not the plugs or timing usually. just from what ive read so far its your carb. the reason it runs good when floored is the secondaries open up and give it fuel when u back off they close and your primaries arnt feeding sufficient fuel. Rebuild your carb first before chasing other things. One thing at a time so you can see what fixes it. i had a quad on my race truck and the motor started poppin and missing. showed all the signs of a lobe gone on the cam. turned out to be a half pluged jet on the primary, changed carb bam good as new.

My 2 cents
Curtis

[kevmic28]

yeah I was just back tracking on what I did before it started running bad to the point that I couldnt drive it, it was plugs and coil. its all got to stem back to the material from the inline filter I found in the carb filter.
Im just working this out loud here but in theory the filter is spring loaded so in the fuel pressure gets too high the filter is pushed back against that spring and the fuel bypasses the filter. So the crap could bypass the filter also.
The timing was off a little.
Ok I will pull the carb tonight when it cools off. Im beat from working on the truck in the heat of the day.
Also the plugs are the right ones for my truck just a little hotter than the others.