Just had completed a full engine rebuild of my stock 2.0L (with Webers) to a 2.3L by a small Porsche indy in Maryland (2.256 big bore, 10:2:1 compression, mild cam). Carbs were also rebuilt to accommodate new build. Unfortunately, engine runs like crap with incessant backfire out of exhaust and carbs (during both acceleration and deceleration). Hard to even really tell yet how the increase in displacement feels due to the bucking and backfiring. However, I do know that power seems to peak at mid 4K range. Planned to have dyno'd but until this is resolved no point. Their estimated build time of 2 months took 14 months and still not drivable so I'm a bit frustrated. Indy acknowledges that he doesn't know what the issue is. Said he suspects its carbs but not certain. Wants me to invest in a new set. To be clear, the carbs have worked perfectly for the last 10 years up to the day i dropped off to their shop. Indy acknowledges no issue with carbs when he received. Frankly, I've lost all confidence and contemplating having another shop look at this issue and resolve. In all fairness, this is not a hack shop...very reputable. I don't want to bash/mention names. Requesting recommendation of an indy, ideally in Maryland, that is capable of assessing and hopefully fixing the issue.

This sounds like a timing issue. What type of distributor are you running? have you verified that all spark plug wires are connected, and in the correct firing order on the dizzy?

Care to share who the Indy is?

I'm not an expert, but am knowledgeable in dual carbs and have quite an assortment we can run through as far as jetting. Bring it on up and we can run it through some tests.

I thought possibly a timing issue and its interesting they have not mentioned this as a possibility...focusing only on carbs. Not sure about type of distributor. I attached pic...maybe you're familiar? I have not verified spark plug wires/firing order with them.

Click to view attachment

Thanks. I'll message you name of shop however I wish to keep that out of the forum post for now.

Sorry for your misfortune, but these things do happen. Do you have the ability to check things like spark timing, valve clearances, compression values? Keep us informed of your findings and it's unfortunate not everyone out there will stand behind their work.

Many fuel related issues are timing issues.
Set dwell/timing before messing with carbs.
Good luck!!

Just looking at the picture tells me the plug wires are wrong or the distributor is not in the 'normal position' for these engines. Wire one should be on the left driver side in the picture. Looks like it is heading over to #3. It could just be the way they stabbed it but backfiring like that makes me think wires are off position.

Will look into. TY

Interesting. Will verify if correct

Simple things first, understand the frustration and concern but the suggestion to make ignition and fueling are correct.

Having an separate independent shop - or friend - check compression or even better leak down test if the above doesn't sort it out.

Hang in there.

yes looks like wrong spark plug wires installation.
Driver side rear: #1
Driver side front: #2
Passenger side rear: #3
Passenger side front: #4

On dizzy: #1 should be at around 11 o’clock (TDC)
# 2 around 8 o’clock
# 3 around 5 o’clock
# 4 around 2 o’clock

you get the idea and sometimes TDC changes which should follow #1 also and same with others.

Click to view attachment

The distro looks to be a Mallory. I believe when I ran one in my 2056 it was 180 out, so the plugs might not be wrong here.

As said, timing, Carbs linkage sync'd (If they messed with the linkage, that would be a major player), Carb adjust.

Great advice all, thank you.

I failed to mention that both times I went to pick up car the indy said he drove it earlier and it ran great. In both instances it ran horribly for me...exhaust backfire, carbs popping, bucking, etc. all the way home (25 minutes). I sent him video recording of my drive home last week that captured the constant backfiring...he said he experienced none of that. How is that possible?

Yes, I believe it is a Mallory. Regarding linkage, they redid the linkage set-up. They also installed new idle/main jets and 32 Venturis. Replaced floats, carb seals, etc

Only thing I can think of is cold engine ran, warm didn't, but I don't think that is the case hear. A stuck choke shouldn't cause those symptoms. Two wires off will. I had two wires off and it idled just fine but as soon as you gave it gas it was awful.

Someone thought the Yugo was a good idea...Anything is possible if he didn't get it warm running it around the block. Weird stuff can happen when they warm up. Valve lash too tight, engine gets hot and valves are left open. Coil going bad, first it runs fine then it gets hot and car runs like crap. All sorts of stuff can happen. Don't beat your head against a wall, start at the beginning. Good luck.

it could be a bad coil on the way out. looking at your photo it looks new.
some do come out of the box not good these days?

it could also be any of the other things.

to be fair to the engine builders sometimes these things can be confounding.
they will run the car and it won't do it for them.
but this does sound a bit like they should have got it good and hot and driven it for 20 minutes/half an hour.
properly test driven it.

if they get the faults up then its going to take a good mechanic with a good instinct for where to look. i would judge them by their reaction to the issue once they have made it happen. if necessary take one of them out in the car with you and drive it until it does it with the mechanic in the car. and then see what the reaction/comeback/opinion is.

and make up your mind about them.

stay cool and don't lose your confidence.

Adding more info OP supplied in a PM-

"The engine idles smooth and revs smooth."

So bucking, popping, backfire, under load could point to a weak ignition system. Better to check that coil. If you have a spare throw it in and try it, would only take a few minutes. You can also check that one with a meter.

I had a funky distributor that I had similar problems with- It was dry when I took it apart- I added gear oil and it smoothed out

Yeah, first, double check the plug wire order, then double check the timing, then check the coil. I like that weak spark idea and hot coil. Coils work great until they just don't all of a sudden.

Come to think of it, double check that the plug wires are actually firmly on the spark plugs and in the cap (same for the coil wire). I have had them loose and ended up with random backfiring etc (thank god not on my 123, I hear that will destroy a 123).

you need to start at square one. With a compression and displacement increase nothing as it was run before will be correct. Start with basics. Are there any vacuum leaks. Are plug wires on correct. Is point gap and dwell correct. Is the timing at idle and full ignition advance correct for your 10.2 to 1 motor (original was around 8 to 1) Are valve clearances correct. Then move on to is carburetors. Are the linkage synchronized and correct. Then tune with wide band O2 to see if idle, part throttle and full throttle jets, venturi etc are correct. Lots of stuff to fiddle with and since non stock you cant just use stock settings.

john

Is 32 venturis big enough for a 2,3 with high compression?

I put CB performance kits in my 40's. The ventures are 34's and they are on a
warmed up 2 L.

I just got hung up on that it idles fine but doesnt work when driving. I agree with many others. Get yourself a notepad and start checking everything and make carefull notes of what you have checked and what you have measured. No sense in spending money on guesses.

Compression, are all cylinders equal within reason
Leakdown, any oddities?
Fuel pressure, within spec?
Timing,
Distributor and ignition leads installed and hooked up correctly
How does the spark plugs look, are they wet or sooty etc, make notes
Air leaks, both topside and bottom (exhaust side)
Carbs and linkage, sync between banks, measure drawn air with a synchrometer
Carb jets etc

There is no magic ticket, its just systematic fault elimination and keeping notes.

Pull a Jet stack and Idle jet and let us know what you are running. Are these Weber 44idf or 40 idf? You already mentioned the Venturis size was Reduced to 32?
Once you get the basics baselined you may want to borrow a wide band O2 to see what is going on wit the carbs. Popping sounds like you are lean
What do the plugs look like? You can set them up without The O2 but just takes a little trial and error

Lots of guessing always happens on posts like these. I need to figure out a way to start some sort of over/under betting pool when these posts pop up. How many guess until the solution for the root cause is properly identified?

Placing call to Vegas casinos now to get in on the action . . . .

I've always kept a journal style notebook for each of my cars. Maintenance info, engine & suspension tuning info, and troubleshooting info. You'd be amazed how handy it becomes to have that history years later when it's all but long forgotten.

That's a Mallory Unilite for the dist. Usually, dimpling the tin around the dist is required to fully seat It. They can be picky about the SP wires. What is your idle RPM? Shoot for 950. Just use one idle speed screw to raise the idle. The rest of the linkage will follow suit. For the displacement I think your Venturi are too small. My 44s have 32mm Venturi installed for a 2056. Lastly, what type of fuel pump are you using? Lots of variables to sort thru.

Your mechanic set the idle and maybe never drove the car. I'm sure it's fine under no load.

I very much doubt that this is a mechanical problem. That said.
1) did the builder do a cam break in?
2) did the builder do a ring break in? (this may be something that you are expected to do.)
Now its your turn:
1) check the basics. Do valves. Do compression.
2) you need to note your carbs. Find out the size of your: Mains, Idle, Vents at least.
3) get a balancing snail and check balance between carbs at hot idle and at 3K rpm.
4) Do all the stuff mentioned in the previous posts about checking timing.


PS: my Vegas bet is that the builder set the timing and balance with the engine and carbs ice cold. Like overnight, below freezing cold. Its been a cold winter in the MidA. As soon as they warm up it all goes to shit and you have an unhappy engine. Once set while warm, the engine starts behaving much nicer.

Zach

Hi Zach - What shop would you recommend? Maryland...possibly PA? You know my limitations;-)

Bring it on up to Mount Airy, we can take a look.

This is the worst time for a shop. Everyone good will be slammed with spring in the air.

I'd go back to the shop you got the car from. They need to have the chance to make it right. When it comes down to it its probably something relatively easy, and they should put you at the front of the line when they do so.

Zach

Or do this. Nick has the know-how.

Zach

Thanks Zach

Sent you PM Nick

Hi,

If that is a unilite, the tin needs to be massaged so that it seats properly. On my build, I had to reindex the distributor gear (I have a vacuum can on mine). Other things to think about.

It is quite likely it is used. There also were QA issues with later Unilites.

1.TDC on #1
2. Pull distributer. Check for grey/grey springs.
3. Compare the drive gear to this pic. Look good. reinstall distributor and rotor. Rotor points to #1. If it's 180 out the gear is installed incorrectly. Use a magnet to remove the spring and reinstall the gear correctly.

Time it and go. If you're not getting 22 degrees total advance, I can lend you the adjustment keys.

I looked closely at your picture. The gear is not indexed correctly. 180 out. You need to confirm that you have spiral wound plug wires. You will cook the optical rotor. Good luck,

Carlos

Or, install the plug wires starting on true #1 in the correct order if you're in a hurry. I mark the Firing order on the cap terminals with a Sharpie.