So I have searched the forum (and internet) before posting...sorry if this a tired old topic.

Trying to narrow down the cause for some backfiring through the carbs and rough running.

Compression: #1-125, #2-90, #3-70, #4-85

Some oil around the air filter housing.

#3 plug fouled so all were replaced.

Carbs synched

Valve job completed.

Still: runs rough in lower RPM ranges especially when starting out and now I'm getting an occasional backfire through the carbs under acceleration.

Mech says it caused by low compression and needs at least a top end rebuild.

A lot of what I'm reading points toward...well a lot of things, but nobody says low compression causes the chugging from start and the backfire.

Agree? Disagree? Not enough info? Thoughts please...thanks!

sounds like your mech might be on the right track. Those are terrible numbers.

Valve job completed meaning valve adjustment or replacement?

So... When was the last time it had the valves adjusted?

If recently, then I agree its probably time for a top end rebuild.

Zach

I also have terrible compression numbers, and I also had a lot of backfiring. I got rid of most of the backfiring through some combination of new rotor and cap, adjusting valve clearances, adjusting timing and syncing the carbs.

Now I have terrible compression, but no backfiring. I call that a win!

Thanks guys! I have accepted the inevitable

Old trick and not sure just how reliable it is as far as firm diagnostics but repeating the compression check on #3 after adding some oil can give you an indication of if the loss of compression is due to rings or valves. if you see an increase it suggests rings.

But with the backfire, I would typically think valves would be the more likely cause. There are a lot smarter people than me here but with 3 of 4 very low I would have to go back to rings.

Keep us posted.

How easy is it to do a leak down on the type 4 in place? Not that it probably matters in this case, because the inevitable seems...inevitable.

A leak down has been completed as well.

Well its all over except for the turning of the wrenches!

What engine is it?

It is a 1.8 with dual Solex carbs. I'll upgrade to big webers at the same time.

Are you going to build it?

You did not answer the questions about valves. What do you mean by valve job? Were the heads removed and taken to a machine shop? Or were they just adjusted? Your symptoms do sound like seriously misadjusted valves. Did your mech do them, or did you do them yourself?

Btw, you know we like pcs, right?

Don't put big carbs on a 1.8 unless the engine warrants it. Bigger does not mean better in this regard.

Zach

It was a valve adjustment done by a mechanic.

Point taken on the carbs.

Thanks!

So thought I'd follow up. I started this thread in May and as of yesterday I finally got the 914 back with a little 2.055 liter hot rod. Took a LONG time, but I'm enjoying it.

Great ,but we are funny on here lots of pics and replies to what you did to get the motor sorted are always welcome viewing and reading, a lot of folks are receiving help on sorting engine issues and that's what its about .

Yeah, post up your combo and build pics. I'm assuming you built a 2056 and not a 2055 (96mm pistons and a 2L crank?)
What cam?
Carbs or FI?

I have a 2056 in my car and I love it. Enough power to keep up with most mini-vans. Lol!

Zach

No pics. Didn't happen!

you say "valve job" did you mean vale ADJUSTMENT? If adjustment and you know that the adjustment is correct, and still low compression then certainly a rebuild. Carbs are very hard on a 914 engine.
So without decent compression trying to get your engine to run correctly, is probably futile, although with carb rebuild, adjustment, no intake leaks, dwell and timing and a good ignition system, it will run better than it is now,

I'll gather what I have tonight if I have time! Sorry for alert haha

Do a leak down test it will tell you exactly where the compression is being lost

[quote name='dr914@autoatlanta.com' date='Dec 12 2018, 09:51 AM' post='2673251']
you say "valve job" did you mean vale ADJUSTMENT? If adjustment and you know that the adjustment is correct, and still low compression then certainly a rebuild. Carbs are very hard on a 914 engine.
So without decent compression trying to get your engine to run correctly, is probably futile, although with carb rebuild, adjustment, no intake leaks, dwell and timing and a good ignition system, it will run better than it is now,


Doctor 914,

Can you elaborate on what you mean by "carbs are hard on a 914". ? Very curious.

Ansbacher