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Guest Message by DevFuse
 

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Weber install: backfire from intake.


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65 replies to this topic

#1 TheYeti

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Posted 13 August 2007 - 11:30 AM

I have searched for similar issues, but have had no luck. Most of what I found had to do with after-fire (exhaust) rather than back-fire (intake) issues.

I have the Weber 32/36 DGEV from Redline installed on my '84 GL w/ EA81. I prep'd the gaskets with seal. The EGR is hooked up. All of the other emission stuff (vac mess, etc...) has been removed. The fuel pressure regulator is installed and set to 3.5 psi. The timing has also been set. The engine will now start and it will idle smoothly, but back-fires through the intake when the throttle is applied. If throttle is given under load the engine continues to backfire with more frequency and eventually sputters out and dies. A few of the local guys ( Thanks Tom, Shawn, Jerry, et. al.) have tried to adjust the mixture, but we just can't seem to get things to run correctly, let alone eliminate the back-fire issue.

I do not know what jets come from Redline Weber in the kit. Given the altitude of Denver CO, could this be the problem, or is there something simple I have missed?

Thanks all,

j.

#2 VaporTrail

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Posted 13 August 2007 - 01:38 PM

how many turns is your idle mixture screw turned out?

what's the psi of the fuel pump you installed?

did you pull the fuel line nipple from the hitachi, and put it on the weber so you have a return line?

#3 TheYeti

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Posted 13 August 2007 - 02:34 PM

The fuel line nipple is from the old Hitachi w/ the return line.

The fuel pump is stock w/ the aftermarket regulator set to 3.5 psi.

I can't remember how far out we turned the mixture screw, but in or out, the back-fire was consistent when ever the throttle was opened up. ( I will follow up on this part though. )

#4 Reveeen

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Posted 13 August 2007 - 03:12 PM

All of the other emission stuff (vac mess, etc...) has been removed.

Vacuum advance to distributor? and if it is hooked up, is it working?

#5 TheYeti

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Posted 13 August 2007 - 03:14 PM

All of the other emission stuff (vac mess, etc...) has been removed.

Vacuum advance to distributor? and if it is hooked up, is it working?


The vacuum is working (can feel it on my finger) and it is hooked up.

#6 Reveeen

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Posted 13 August 2007 - 03:17 PM

I would check the "business end" (the diaphragm) in your distributor, followed by a mechanical advance check (grab the rotor and see if you can move it against the springs) and a timing check.

#7 Jerry DeMoss

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Posted 13 August 2007 - 06:58 PM

If I remember correctly the mixture screw is sitting a 1 1/4 turns out. Also the timing should be right on the mark right now since Shawn worked his timing magic, since he is a 4th level subaru wizard.;)

I was thinking about this a little more and sometimes cough through the intake can be from a lean condition and out the tail pipe is generally from rich condition. I will have to look through my weber book some more.

#8 Carmen

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Posted 13 August 2007 - 08:24 PM

can be the pcv valve??

#9 VaporTrail

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Posted 13 August 2007 - 08:42 PM

the rule for the mixture screw is start 2 turns out I thought... I used to run mine at almost 4 turns out....

you shouldn't need a pressure regulator with the stock pump, only if you have an aftermarket pump that puts out too much....

#10 Tom63050

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Posted 14 August 2007 - 12:54 AM

I do not know what jets come from Redline Weber in the kit. Given the altitude of Denver CO, could this be the problem, or is there something simple I have missed?


This is the jetting I had. I ordered the Redline kit for a '78 VW bus, 1800cc. Later I switched the Weber to my 84 Sube wagon & it ran fine.
............................. Primary...Secondary
Main (fuel)................140..........140
Idle.............................60............55
Air correction............165.........160

The Weber book I had said that the main jets should be reduced by 5 (i.e. from 140 to 135) between 5000 - 6700 feet, and 5 more from 6700 - 10,000 feet. This keeps it from running rich in the thinner air. Reducing the primary seems important to me, but I doubt the secondary matters much, unless you have a heavy right foot.

But I think none of this has anything to do with your backfiring problem, just good info to know.

#11 Cougar

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Posted 14 August 2007 - 04:00 AM

Has the disty been checked to see if it is a tooth off?

#12 TheYeti

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Posted 14 August 2007 - 06:27 AM

Wow! Nice way to wake up :) Thanks for the responses everyone.

Mc, I know we did not go much past 3 turns out...

I may have time to go try and fiddle with things again later this week, so I will keep you all posted.

#13 TheYeti

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Posted 16 August 2007 - 01:38 PM

Ok, I played with the mixture screw a little more today. The backfire now occurs after I rev it and let off the pedal. I give it some gas after that and "pop", around 1-2k. It will also give a backfire when under load.

Sound like a lean condition?

#14 Jerry DeMoss

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Posted 16 August 2007 - 01:45 PM

Ok, I played with the mixture screw a little more today. The backfire now occurs after I rev it and let off the pedal. I give it some gas after that and "pop", around 1-2k. It will also give a backfire when under load.

Sound like a lean condition?


Were you able to drive it a bit? I might give ya a call later if I think of something. Did you get a backfire from the tail pipe or out the carb?

#15 VaporTrail

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Posted 16 August 2007 - 03:10 PM

Were you able to drive it a bit? I might give ya a call later if I think of something. Did you get a backfire from the tail pipe or out the carb?


how do you have the throttle return spring installed? sounds like fuel is still dribbling actually, not lean.....

#16 Jerry DeMoss

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Posted 16 August 2007 - 03:19 PM

how do you have the throttle return spring installed? sounds like fuel is still dribbling actually, not lean.....


There is no external return spring other than the one already on the carb if that is what you are asking. I thought about that also.

#17 VaporTrail

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Posted 16 August 2007 - 10:30 PM

There is no external return spring other than the one already on the carb if that is what you are asking. I thought about that also.


should probably put one on. Mtn Grizzly was running oddly, idle was all over the place...backfiring through carb... the spring had come off. replaced, and back to normal operation...

#18 TheYeti

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Posted 16 August 2007 - 10:52 PM

It makes sense, but finding a spring? :)

#19 Jerry DeMoss

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Posted 17 August 2007 - 12:29 AM

It makes sense, but finding a spring? :)


That is what old matress' are for!;) I think we can find something since you seemed to figure out your throttle cable mounting bracket very well.:)

#20 TheYeti

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Posted 17 August 2007 - 07:37 AM

Colonel still backfires under load... I don't think it is the spring.

#21 VaporTrail

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Posted 17 August 2007 - 09:07 AM

valve clearances correct...?

was the carb put on a previously fine running engine?

vacuum line from disty to the front of the carb?

can you post a large detailed pic of the carb and connections?

#22 RelicGL

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Posted 18 August 2007 - 02:32 AM

valve clearances correct...?

was the carb put on a previously fine running engine?

vacuum line from disty to the front of the carb?

can you post a large detailed pic of the carb and connections?


Somehow, the float level in the fuel bowl comes to mind. Make sure it's set properly and that shipping turmoil doesn't have the float stuck at the top.

If that's the case, put everythiong else on the carb back to a base starting place, ie the mixture screw set back to 1 1/4 to 2 turns and go from there.

#23 TheYeti

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Posted 24 August 2007 - 08:20 AM

I haven't had a chance to get back to the shop in the last week or so. The wife and I have been working to get a house and it has been a little more than crazy!

I will remember to re-check the float level, etc... If none of that works, I will try to get the altitude jet kit from Redline and go from there.

#24 TheYeti

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Posted 24 August 2007 - 10:33 AM

Something else I started to think about: When I originally installed the carb, I noticed that the mounting adaptor plate from Redline is not exactly "flush" with the inside edges of the EA81 manifold (off by quite a bit in some places). This might cause some issues with flow from the carb to the manifold.

Could this be the problem? Would it hurt to go back in and grind the inside of the adaptor plate to be more flush with the inside of the manifold?

I hope this makes sense.

#25 VaporTrail

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Posted 24 August 2007 - 11:04 AM

Something else I started to think about: When I originally installed the carb, I noticed that the mounting adaptor plate from Redline is not exactly "flush" with the inside edges of the EA81 manifold (off by quite a bit in some places). This might cause some issues with flow from the carb to the manifold.

Could this be the problem? Would it hurt to go back in and grind the inside of the adaptor plate to be more flush with the inside of the manifold?

I hope this makes sense.


you can go back in and grind off to match them, but I've used both ways without issue....

any chance to get a detailed pic?




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