backfire problem 1.8 w/new carbs

[earlr85944]

it dont come easy........
well new carbs are in, went from progressive 2bbl to dual webber 34's
problem is drivers side backfires up thru the carb no matter what i do to the carb adjustment. Im thinking valve adjust time? What get me is it ran fine with the single carb(other than an occassional stall due to a throttle shaft leak)
according to the weber adjust manual, i need bigger jets as i need to turn the speed screew in too many turns but why backfiring on one side?
BTW- idles nice,and has power when opened up but backfires on the left side only during accelleration.

[earlr85944]

any more ideas? i tried to adjust the carbs at idle and they are balanced w/ synchrometer and now matter how rich or lean i make that one carb it backfires upon acceleration...

[Dave at Pelican Parts]

Vacc leaks, most likely.

--DD

[earlr85944]

I checked for leaks at the carb and manifold and didnt find any. i also installed the vacuum hose that helps equalize the vacuum between manifolds, no change.
I checked sync between the carbs at idle which was fine then while accellerating and there is a dead spot where the carb that is backfiring opens sooner than the other side, guess its time to play with the linkage, would that cause a backfire up into the intake?

[earlr85944]

totally lost now, swapped carbs side to side, no change
adjusted carbs and linkage. no change
checked for vac leaks, found none
cleaned cap. rotor and adjusted points, played with timing, nothing

any thoughts, i dont have a plan B

[Dave at Pelican Parts]

You swapped the carbs from the left side of the engine to the right side, and the same side of the engine still popped and spat?

If so, ignition and compression are where you should be looking. Valve adjust, compression test, checking cap/rotor/plugs/wires/points.

--DD

[earlr85944]

sounds like a plan, I now am thinking that the prob was there with the single carb but was masked with the long intake runners.

[Joe Ricard]

Yep. it's not carb related.

How are you checking for vacuum leaks?

I use starting fluid the engine speed change is instant.

[GBG1000]

I recently had a dual weber 1.7 start running terribly, on 2 cyls. You can search for my thread and read the whole story. Short story is I rebuilt the carbs and it was like night and day. Runs great now. Are your carbs new or just new to your car?

[earlr85944]

brand new from weber, its not looking lke a carb problem now.
I did a compression check and got
1- 120
2-110
3-120
4-130
or pretty close to that, just going by memory, nothing raised a flag when i did it.
Poped the "bad" side valve cover, im going to check the valve adj next.
I may pll the heads just for GP being im in this deep already, it seems like the heads can be removed with the motor in car, is that correct?

[Dave at Pelican Parts]

Not really. There's not enough room to slide them off of the head studs without dropping the engine below the level of the chassis.

If the compression is good, that's definitely a good sign. Check that valve adjustment, then start concentrating on the ignition stuff. If that isn't the problem, then check out the fuel delivery to the carbs.

--DD

[earlr85944]

YES PROGRESS! Adjusted the valves on the "bad" side, the intakes were a little tight @ 1-3 thou too tight the exhausts we good at 6 thou. Started it and basically the same prob, then i remembered the artice that is posted in the tech area about timing for carbs, so I set the timing as per the "other" mark on the fan. Now it gets better: idle is nice, and hitting the throttle is smooth till @4500 rpm then a slight popping, still from the dr side. So I readjust the carbs as per the weber docs and go for a ride, slight poppping but nothing like before, so I say hey lets open her up and she starts running like new money! Plenty of power no popping pulling like silly! Good to go! Thanks all for you expert advice!

Now more questions, after adjusting the valves I see my haynes book say .008" for the exhaust valves? Alot of other docs say .006?

Next, can someone recommend a new distributor for the car, I have the stock one in right now with points and it needs to go.

Any thought on the manta exhaust? 4 tips 2 mufflers, will this hurt the low end as im planning to use it for A/X

[Dave at Pelican Parts]

Haynes is wrong for the 1.8 exhaust; use 0.006".

The stock distributor is fine for carb applications. Going better is gonna get pricey in a big hurry--check the Mallory distributors. They're evidently about the best, and they are not cheap.

The Manta exhaust (and similar ones) will generally hurt performance slightly over stock or the Bursch, but are OK. They tend to be loud and rust easily.

--DD

[earlr85944]

cool, thanks for the info and the help Dave. I will just leave well enough alone and enjoy what got

BTW, do you think its a good idea to get rid of the points for an aftermarket pickup?

Also, would an msd 6a help much?

[Yahow lam]

My '74 2.0L with rebuild heads and new rings is doing the same thing, in addition it also has white smoke when it sit at idle for a while but do not notice the smoke when I am driving and the acceleration is not smooth and I check the dwell is off @30 you think that may be the problem? I read the old articles in this forum it mention check the CHT please tell me what is that stand for.

Thanks, Yahow

[Dave at Pelican Parts]

CHT == Cylinder Head Temp; it's a sensor for the fuel injection. (The OP's car has carbs, not FI. Don't know about yours.)

Back on topic: I hate points. I figure any way you can get rid of them is a good thing.

The MSD can help keep from fouling plugs if your mixture is a bit over-rich, but don't expect miracles. It may make the idle a bit smoother.

--DD

[Yahow lam]

Dave, mine is FI and thank you for your info.

Yahow

[earlr85944]

any suggestion on what hardware to use to replace the points?
BTW- running better than ever, I did advance the timing a bit from the recomended carb advance, it seemed to reduce engine temperature.

[Dave at Pelican Parts]

Pertronix, Compufire, or Crane for the points-replacement. Pertronix and Compufire are magnetic hall-effect systems, the Crane is optical.

Or just replace the distributor with the Unilite. More money, but it's supposed to be the best thing you can do for your carbed 914 motor after bolting a Tangerine Racing exhaust onto it.

--DD

[earlr85944]

WOW, after checking these products I realize the only thing my 914 budget permits is a points file!

OK so ill splurge a bit and go for the Crane, THX again!