l20b new weber no acceleration

[nathan_454]

just put a weber on my l20b and now i cant hardly accelerate... it bogs when i try... could this be air screw?

[izzo]

just put a weber on my l20b and now i cant hardly accelerate... it bogs when i try... could this be air screw?

 

 

Maybe, but also make sure its seated properly. Even a small vacuum leak will cause it to run like shit and bog under acceleration.

 

For the air screw = Let it warm up, turn in till its barely running, then turn it back out till it clears up. Then do another half turn. Good to go.

[nathan_454]

Yeah ive done exactly what the manual says. I have checked for vacuum leaks and the only i can find is when i spray brake clean at the base of the carb it isdles up just a little bit... I dont dare tighten the mounting nuts any tighter though... should i think about putting rtv?

 

what it does no matter which way I try adjusting the idle screw is it will bog when trying to accelerate. and if I give it too much fuel it will start popping out the carb like a backfire. the timins is correct right at 12 degrees.

 

the only way to get it to accelerate is to just lightly barely give it any throttle, staying under the point at which it starts to bog. which is about 1/8-1/4 throttle.

[nathan_454]

after reaqding the weber tuning guide and the vacuum leak tech page it sounds like that is whats creating my problem.. i guess I will hunt down and try to fix them all tommorow

[bananahamuck]

Im pretty sure i have a couple extra base adaptors laying around if you think yours might be warped or something.

[nathan_454]

it shouldnt be i just put the freaken thing on brand new out of the box on friday

[izzo]

it shouldnt be i just put the freaken thing on brand new out of the box on friday

 

 

New or not, it could be warped or be cracked? I had to tighten mine down quite a bit on my truck. Unhook the stuff, take the carb back off. take the adapter off, check the mating surfaces for any debris. Put the lower gasket on, set the adapter on, make sure you get the two screws in nice and tight, then make sure the studs are ok. Set the carb back on there, and make sure it goes on easy. You shouldn't have to fight it! Wiggle it around and look around make sure it looks nice and flat, then re-tighten them. Sounds like a PITA, because it is lol. just take your time and have some patience, it pays off. once its on there good, hook up the gas line, and vacuum advance. Make sure theres nothing else that could be leaking (brake booster??) Then try and run it again.

[I'm BLUE]

shouldn't have to "crank" down the nuts/bolts especially on carbs ,,,, just a few ft lbs and thats IT !

[bananahamuck]

Also try sucking on vacuum advance with cap and rotor removed the plate should move a little.and the hose is connected at the bottom most port in carb.

[bananahamuck]

,(((edit)))Will be going to billetproof drags in toutle so I will leave adapter in big white cab over in front yard if ya need it ,,are you using tah manifold we found in yard cause maybe the base of it is warped and needs filing??file-ing??

[datzenmike]

Running lean from a vacuum leak can back fire through the carb. Is the carb new as well?? Check that the secondary is fully closed at idle?

[nathan_454]

yeah its a new carb... all the symptoms lead to a vacuum leak.... heres a question, isnt the pcv in effect just a big vacuum leak?

[benson64L]

Im having a similar problem but i have the original carb that i just got rebuilt. After i got it rebuilt i used new gaskets but not a new base plate. The truck ran for about 2 months and now i am experiencing the same symptoms. Would it be worth tryin? And were is a good place to get new gaskets and base plate?

[banzai510(hainz)]

acell pump working?

 

Look imside carb and give it gas. You should see gas being squirted in the main barrel from the top.iF NOT THEN THAT IS IT. sometimes the level mak get stuck in the IN mode and not return out. The acell pump diaphram is the square thing on a valve cover side. look closely. a little arm will push and should squirt gas out the top.

 

If it idles then everything it tight and fine. Recheak the timming.

 

I had a point dizzy once and I had the same symtoms. I over torqed the carb bolt end uip cracking the thin weber adapter only to find my point dizzy had a worn bushing which caused it to start poping ,cutting out making it look like the carb.Idf dizzy shaft has alot odf side to side wobble this could be it also. Cause the coil to prematurly fire when not needed.

 

 

also make sure you didnt ovetighten the hex nut on back of the linkage of the weber. It can bind it and cause a stumble. Maybe they bend the trottle shaft. try loosen it up and run it.

[deadmonkey]

Be sure the adapter plate isn't hiting the EGR stuff that bolts to the side of the intake manifold. I had to cut a chunk out of the EGR stuff because it was hitting the adaptor plate right next to the front drivers side bolt. The EGR vacuum was touching a peice on the Carb too.

[datzenmike]

yeah its a new carb... all the symptoms lead to a vacuum leak.... heres a question, isnt the pcv in effect just a big vacuum leak?

 

The PCV valve itself is a small opening maybe 1/16" or so. Engines will run with this and are tuned to account for it. A vacuum leak would have the greatest effect at idle. If you want to check this pull the hose off and put your finger over the opening and try revving it up.

 

Is the vacuum hose to the brake booster loose or leaking?

[nathan_454]

It idles awesome. nice and smooth... and it will rev if I do is slowly. if i try to blip the throttle it will backfire out the carb. I have checked and rechecked the timing. it seems good at 12 degrees. I did notice one time that after i had set it to 12. ran it for awhile and then rechecked it it was at almost 0 degrees. so i reset it and it has stayed at about 12 degrees since then. when i had the distributor out It seemed to be tight, no bushing wear.

 

the brake booster line seems ok.

 

I dont have egr anymore (i put on an early L non smog intake manifold)

 

the throttle shaft nut that holds the linkage on is not overly tight - the shaft seems to move freely.

 

I have not had a chance to run the truck today. I will mess with it tommorow morning and see what i can find.... perhaps theres someone in the PNW that would be willing to help me out? I'll buy beer!

[nathan_454]

oh and heinz - yeah the accel pump is working.... it squirts gas when i move the throttle.

[datzenmike]

acell pump working?

 

Look imside carb and give it gas. You should see gas being squirted in the main barrel from the top.iF NOT THEN THAT IS IT. sometimes the level mak get stuck in the IN mode and not return out. The acell pump diaphram is the square thing on a valve cover side. look closely. a little arm will push and should squirt gas out the top.

 

 

As Hainz says. With engine off pump the gas while looking down the carb. You should see a strong squirt of gas into the main barrel.

 

If this is fine, check that all valves have at least some clearance and haven't tightened up..

[nathan_454]

well I just found a pretty major vacuum leak. at the base of the carb adapter - the screws had worked loose ( I guess i didnt tighten them enough). it would almost kill the motor with a 1 second shot of brake clean under the adapter - so i took the carb off and the adapter off - rtv'd the gaskets and reinstalled the adapter and carb - this time with lock washers (the inside carb mounting nuts werent very tight either) so now its setting up and in an hour or so ill start it and check again...

 

the accelerator pump is working - I can see a strong stream when i work the throttle.

 

I adjusted the valves while I was waiting for the carb in the mail so they should be good. I will re-check if the problem continues but doubt they are the culprit.

 

all my symptoms led to a vacuum leak, and i think i may have gotten this one sealed up... will report back my findings.

 

thanks guys

[datzenmike]

Nope if you found the leak that will be it. I've heard of these bolts coming loose so try some Loc Tite on them.

[nathan_454]

I should have put loctite on when i had it apart. oh well i tightened them down pretty tight this time. last time i was apprehensive about going too tight. i guess if they work loose again i will loctite em

[datzenmike]

This is likely why people crack the adapter. They have to re-tighten them and get carried away.

[nathan_454]

yeah i can see it being easy to do. I dont like the idea of having to tighten the two outside screws that hold the adapter to the manifold and not being able to tightnen the inside studs until the carb is set on... not able to walk it down a little at a time like i would like to do.

[nathan_454]

ok so i now have NO vacuume leaks. it idles better and was able to get the idle down to 900 rpm stable (was unable to before)...

 

BUT - it still pops when you try to give it too much throttle too fast... I was able to watch it, and when it is backfiring is as soon as the secondarys start to open.

 

I can also make it do it by working the secondarys alone... every time they open it pops out the intake. even if i ease into the throttle slowly. once it gets to opening the secondaries - it pops!

 

WTF is going on here????? im getting pissed at my brand new high dollar carburetor!

 

is it something i am doing? is there somethign wrong with my carb? WTF WTF WTF