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Old 03-06-2004, 11:08 PM   #1 (permalink)
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Backfire/hard To Start Woes.....

little bit stumped on recently out of shop 9/69 fj40.

carb is new weber, recently installed and adjusted by mech.
valve job and valve adjustment less than 2 months ago. less than 100 miles put on the 40 since i got it out of the shop.
new distributor installed with valve job. timed by mech as well.

usually it is hard to start like the carb is not getting gas, sluggish once started but after it warms up runs fine. usually has a slight hestitation in first gear from complete stop. recently replaced the fuel filter.

WAS only backfiring/"dieseling" thru carb when i shut the engine off. PO plugged the vent line from the newly installed rear steel gas tank. once i discovered this i recently vented same thinking that this was the problem. now it is backfiring thru the tailpipe only upon shutting off iginition.

wondering if the fuel pump is having problems drawing necessary fuel length of approx 8 feet of fuel hose ? if so would a electric fuel pump solve the problem, if the carb is not getting sufficent fuel, and causing it hard to start and backfire ?
should i re-check/adjust the timing now that i vented the fuel tank ?
is there a anti backfire valve on a weber ? ps> has an electronic choke wired via the alternator.

thanks any ideas.. !
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Old 03-06-2004, 11:18 PM   #2 (permalink)
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Backfiring out the tailpipe is too much fuel or ignition problems. The superheated fuel ignites when it comes in contact with the oxygen rich air outside the exhaust. This can also happen when your engine continues to turn with no spark present. The F engines will even run backwards sometimes if the compression is low enough. Have someone turn your ignition off while you watch the fan. See if it kicks backwards after the key is off and also how long she spins. All this motion draws fuel through the engine.
The hard starts could be timing if the engine labors to turn over(too far advanced) or more likely, the choke isn't set correctly. You need more fuel to start an engine because the fuel condenses on the sides of the manifold when it is cold instead of atomizing.
The slight hesitation could be a lean condition or you are running too rich. Lean will feel like a sudden loss, whereas rich feels like a gradual one. We run the 38/38 Webers, haven't figured out the 36 Webers yet but I figure they are similar.
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Old 03-07-2004, 09:11 AM   #3 (permalink)
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questions...

WHAT ABOUT A "pro fuel regulator" WHICH HAS BEEN RECOMMENDED BY ANOTHER CRUISERHEAD TO SOLVE THESE PROBLEMS. DOES THE WEBER 36 COME WITH A REGULATOR ALREADY ? I HV AN ELECTRONIC CHOKE ON THE WEBER, IS THAT ADJUSTABLE ?
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Old 03-07-2004, 01:51 PM   #4 (permalink)
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hard starts

I'm with Treerootco on the timing thing. Too many mechanics that can't or won't take the time to dial in a carb will just advance timing until the motor smooths out. DON'T DO ANYTHING UNTIL YOU CHECK YOUR TIMING. Post results.
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Originally Posted by lc tpi
...if I have to buy them from Trail Gear I guess I dont need them.

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Old 03-07-2004, 05:57 PM   #5 (permalink)
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The electric choke is easy to adjust. There are three screws that clamp the white plastic spring cover down. Loosen those screws and turn the white part. One way will close the choke, the other will open it. With the engine cold, turn the housing so the choke is in the closed position. Turn it just to the point that it shuts. At that point, tighten the cover. Next, you need to locate the screw behind the choke thermostat. This is important because it limits how far closed the choke can go. Too far and you kill the engine under throttle (vacuum sucks the choke closed). This adjustment is made with the truck cold. Start with maybe a 1/8th gap, fire up the engine and adjust for the smoothest idle. As the electric choke heats up, the plate will open.
I run a fuel pressure regulator on my Weber. It isn't needed but I found that the engine has a smoother idle with one. Mine is set for 3.5 to 4 psi for highway and I turn it down to 3 for wheeling.
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Old 03-08-2004, 10:44 AM   #6 (permalink)
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thanks.

thanks for the reply. i hv not had the chance to fiddle with the truck, but my thoughts are as follows :

since the fuel tank was not vented, the carb and timing was adjusted when the fuel pump was having trouble drawing from the tank due to vapor lock. now that it is vented, do i need to adjust the carb again as its getting too much fuel. would the timing adjustment be affected by the above as well ??

the carb was 'dieselin/backfirein' thru the carb only before the tank was vented and now is backfiring thru the tail pipe only ?? any ideas
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Old 03-08-2004, 12:07 PM   #7 (permalink)
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IDEA

Get those timing specs!
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Originally Posted by lc tpi
...if I have to buy them from Trail Gear I guess I dont need them.

65SWB45, 64LWB45, 68FJ40, 72VJ40, 76K5, 73Sub454, 97Sub5.7, 2002 Trailblazer

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Old 03-09-2004, 12:15 AM   #8 (permalink)
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Yep, timing first. BB just in the window at 650 rpm. If you have a vacuum advance on the distributor, pull it and plug it while you are adjusting the timing.
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Old 03-09-2004, 09:15 AM   #9 (permalink)
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timing

If things are working the way they're supposed to, distributor should not have any vacuum signal at idle.
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Originally Posted by lc tpi
...if I have to buy them from Trail Gear I guess I dont need them.

65SWB45, 64LWB45, 68FJ40, 72VJ40, 76K5, 73Sub454, 97Sub5.7, 2002 Trailblazer

tlca #1086
member: Trail Crew-L.A. TLCA, Elwood Chapter, TLCA
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Old 03-09-2004, 09:02 PM   #10 (permalink)
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timing

ok, purchased a timing gun and gave it my best effort tonight.

seeing your above post - i forgot to plug the vac advance, but i did pull it.

cruiser seemed to run best a little retarded (placed the 7 degrees just to the right of the pointer), easier to start and more pickup at higher speeds. does still 'diesel' just a smiggen after killing the ign. going to see how she runs when i go to start her tomorrow am.

let me just get this straight :
1) at idle speed i am supposed to lineup 7 degrees right of the bead/indention/deadcenter with timing light on and vac advance hose off. the bead is jusy inside of the viewing window (left of the indicator)
2) once adjusted, noticed that the dead center mark lines up on the pointer when the vac hose is attached using the timing gun at idle.

correct, did i miss anything ??

oh yeah, engine idles down a little when i hook up the vac advance AND when i increase the RPMs the 7 degree mark moves to the right of the indicator point(er).

please give me your opinions on the above, should i re-adjust with the vac advance plugged ?? will this make a big difference ??
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Old 03-09-2004, 11:32 PM   #11 (permalink)
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timing,starting and carb issues

If your engine lugs with the vacuum connected, you probably have a vacuum retard distributor. How sad! Considering the wealth of options to replace it with a real distributor, you should consider ANY of them a good choice.

As far as the dieseling, what is your idle speed. Can you look inside the primary side of the carb and see fuel dribbling out of the primary. At idle, all necessary fuel should be delivered thru the idle circuit, underneath the throttle plate, and there should be no draw thru the primary. Ergo, when you shut the car off, the idle stop solenoid provides a prompt, complete shutdown. If you can't turn the idle down til gas stops coming thru the primary, you have other problems.
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Originally Posted by lc tpi
...if I have to buy them from Trail Gear I guess I dont need them.

65SWB45, 64LWB45, 68FJ40, 72VJ40, 76K5, 73Sub454, 97Sub5.7, 2002 Trailblazer

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member: Trail Crew-L.A. TLCA, Elwood Chapter, TLCA
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Old 03-10-2004, 09:02 AM   #12 (permalink)
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tuning...

how about the plugging the vac advance for timing adjustment ??

7 degrees off TDC ? this is normal standard for timing ??
my manual did not give the exact settings.
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Old 03-10-2004, 10:44 AM   #13 (permalink)
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timing

Check the vacuum signal on the secondary side of the carb. If it has none at idle, hook the distributor to it, the way it is supposed to be. 7 degrees is factory spec. That is why the ball is there!
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Originally Posted by lc tpi
...if I have to buy them from Trail Gear I guess I dont need them.

65SWB45, 64LWB45, 68FJ40, 72VJ40, 76K5, 73Sub454, 97Sub5.7, 2002 Trailblazer

tlca #1086
member: Trail Crew-L.A. TLCA, Elwood Chapter, TLCA
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Old 03-10-2004, 09:48 PM   #14 (permalink)
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adjusted the timing

i adjusted the timing with the light per 1st plug.
got the BB dead on with the vac line off and plugged.
runs smooth @ idle but still hard to start.

drove it to a friend house and it diesels after shutting off.
hard to start after sitting 25 mins. then was backfiring thru the carb after starting. made it home ok, but was running Krappy.

No fuel from the Primary in the carb at idle.

Tomorrow will adjust timing from the beginning.
I figured that since it was just tuned up, that the distributor was set correctly.
Maybe the mech put it in 180 ? sound likely ??
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Old 03-10-2004, 11:05 PM   #15 (permalink)
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Sounds like you have a vacuum retard distributor. These are designed to work with the smog computer/VSV and are not connected directly to the carb. Just take the vacuum line off and plug the hose at the carb. Probably no need to reset the timing. Spitting back through the carb usually indicates a lean condition; either a big time vacuum leak or bad carb. Hard starting is consistent with not getting fuel. Squirt or pour a little gas in the carb and see if it starts right up to confirm this.
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Old 03-10-2004, 11:21 PM   #16 (permalink)
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Going back thru your posts, I don't see where you say what distributor was installed. Hard starts may also be a sign of a points-dwell problem. Do you have access to a dwell meter? I'd like to know dwell specs (much more relevant than point gap)
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Originally Posted by lc tpi
...if I have to buy them from Trail Gear I guess I dont need them.

65SWB45, 64LWB45, 68FJ40, 72VJ40, 76K5, 73Sub454, 97Sub5.7, 2002 Trailblazer

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Old 03-11-2004, 07:19 AM   #17 (permalink)
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just read this post and thats what I was thinking, the points are out of adjustment. Iknow my45 acts the same way when the points are messed up. Check that, then your timing again.

Quote:
Originally posted by 65SWB45
Going back thru your posts, I don't see where you say what distributor was installed. Hard starts may also be a sign of a points-dwell problem. Do you have access to a dwell meter? I'd like to know dwell specs (much more relevant than point gap)
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Old 03-11-2004, 08:57 AM   #18 (permalink)
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carb and running condition

the dist was just rebuilt and installed by mech.
along with valve job and carb adjustment (weber 32/36).

runs ok at idle and the carb is getting enough gas, after cranking the lots of time the engine starts but in a flooded condition until it burns off some fuel.
it runs but after warming up wants to studder and back fire out the carb while running and after shutoff.

there was a little but if black dust in the carb when i last started it up, around the lip on the bracket to connect the stock air intake.

regarding emissions, its a 9/69 fj40.
there is a small rod shaped vac port on the side wall of the drivers side, its has never been connected since i got the rig. really no emission seem to be hooked up at all.

just recently vented the fuel tank since the PO did not, and yesterday purchased a used charcoal canister to use with the vent hose to limit smelly gas fumes. ran the tube to the canister from the tank, the other to open air.
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Old 03-12-2004, 12:43 AM   #19 (permalink)
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I understand that you may not consider the distributor a possible culprit because it was rebuilt, but I must again request that you obtain a dwell reading on the points. These are the standard steps in diagnosis. If you short circuit the process, then thats what you end up with: a short circuit diagnosis!
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Originally Posted by lc tpi
...if I have to buy them from Trail Gear I guess I dont need them.

65SWB45, 64LWB45, 68FJ40, 72VJ40, 76K5, 73Sub454, 97Sub5.7, 2002 Trailblazer

tlca #1086
member: Trail Crew-L.A. TLCA, Elwood Chapter, TLCA
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Old 03-12-2004, 07:52 PM   #20 (permalink)
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still going, no dwell angle tester =(

still in the process of fine tuning the timing. i don't hv a dwell angle tester.

many hv mentioned about advancing the timing to the point where the engine pings (then retard it back until it stops). i cannot for the life of me, hear the mystry PING. can someone describe it to me... ?

also, does the above go for NON-VAC-ADVANCE distributors ?
i do not hv an advance, only a stock rebuilt vac retard distributor.

presently i hv advanced the timing with the BB just viewable in the window. I did adjust the timing with BB on the pointer, but when i stomped on the gas in third gear it started to miss. it doesn't miss as bad when i stomp on the gas now.

it was dieseling thru the carb after shutoff (with BB on pointer) and now does not do it that as frequently but does knock once after shutoff.

i had the vac connection on the stock distributor connected to the carb but that presented major problems (only applies for vac advance distributors). removed the line and plugged both ends. presently my vac retard stock distributor is not connected to the emissions system as it was designed to. working from mech advance only.

anyone else hv the same setup ? looking for a little more info on timing the engine in this situation. plus info on the mystery ping !!!

thanks !
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