EFI vs Carbs, This will start a crap storm Options

[ellisor3]

I inherited a pair of Zenith carbs on my six conversion I purchased last year. Yes that is Zenith, not PMO or Weber-Zenith. The set-up was done by Motor Scheister several years ago by the PO (IMG:style_emoticons/default/sheeplove.gif) . I have been working with these for the last month to get them tuned and sync'd. I can not for the life of me get them right. They will idle ok but at acceleration they backfire or vise versa. They were rebuilt at AA back in the summer, but that did not solve the problem. No exhaust leak, new plug and the same problems. Some adjustments don't have any effect at all on the set-up. (IMG:style_emoticons/default/headbang.gif) I am at my wits-end on these damn things.

Anyway my delima is whether I should replace the Carb's with PMO or Weber or simply junk the carb idea and move to EFI. Here are some of my considerations, but wanted some I may have missed.

1.) Cost of Carb PMO's $3500
2.) Cost of EFI ??
3.) Ease of adjusting/reliability-EFI
4.) I live in Florida so high humidity-EFI??
5.) Fuel efficency-EFI
6.) Acceleration-Wash??

Thanks for your input

[ahdoman]

We need a little more info to help...
1) What size carbs?
2) What size engine and ignition details?
3) Was the engine originally injection and carbs added later?
or...
4) Was the engine built for carbs?
5) Are they backfiring in the carb or through the exhaust?

[ConeDodger]

PMO carbs are very - very good. Congratulations, yours is the first running motormiester engine I have ever heard of.

[SirAndy]

If the engine was done by Motor Meister, maybe your carbs aren't the problem ...
(IMG:style_emoticons/default/shades.gif) Andy

[McMark]

(IMG:style_emoticons/default/agree.gif) You could easily spend thousands chasing a problem. Sounds like you need to do some more troubleshooting/investigating. Have you done a compression test? Leakdown test? Double checked timing? Adjusted valves?

[ellisor3]

We need a little more info to help...
1) What size carbs?
2) What size engine and ignition details?
3) Was the engine originally injection and carbs added later?
or...
4) Was the engine built for carbs?
5) Are they backfiring in the carb or through the exhaust?

Sorry should have added this in the beginning

The Carbs are 40's
Engine is a '78 3.0, I have not checked the ignition
It looks like it was set up for carbs, no evidence to say otherwise.
The poping is coming from both the carb and the tailpipe, but not leaks that I can find.

Thanks again

[ellisor3]

PMO carbs are very - very good. Congratulations, yours is the first running motormiester engine I have ever heard of.

Running is a relative term in my case.

[ellisor3]

(IMG:style_emoticons/default/agree.gif) You could easily spend thousands chasing a problem. Sounds like you need to do some more troubleshooting/investigating. Have you done a compression test? Leakdown test? Double checked timing? Adjusted valves?

I had the car shipped to AA before it came here and Sean checked it out and did not find any real issues with compression. He said he had this thing set up pretty well when it left AA but when it got to Florida it was FUBAR, maybe because of the drop in elevation, who knows. The engine sounds strong and runs strong except for the popping and backfiring.

[PeeGreen 914]

My engine was doing the same thing you are talking about. NOT THE CARBS. Turned out there were some valve issues and unbalanced issues and ... you get the point. Tear it down and find out what you have before you are out an engine.

[rfuerst911sc]

You say the motor is a 3.0 has the ignition distributor been " setup " to run with carbs? I don't believe she will run great without this being done. I have a 1983 911SC running PMO's and my 914GT clone will be running a 3.0 with 40mm Webers. In both cases I pulled the distributor and sent them off to be completely refurbed AND setup for carbs. They eliminate the vacumn advance and do other internal voodoo to make it play well with carbs. Runs aprox. $450.00 - 500.00 for a real pro to do it.

[jt914-6]

(IMG:style_emoticons/default/agree.gif)
I too have a 3.0 set up for carbs., 40 IDA's. Had the distributor recurved for the engine. They wanted to know what cams I had. Get it set up right and then see how it runs......Even if it is engine related, at least the distributor will already be rebuilt.

[ellisor3]

You say the motor is a 3.0 has the ignition distributor been " setup " to run with carbs? I don't believe she will run great without this being done. I have a 1983 911SC running PMO's and my 914GT clone will be running a 3.0 with 40mm Webers. In both cases I pulled the distributor and sent them off to be completely refurbed AND setup for carbs. They eliminate the vacumn advance and do other internal voodoo to make it play well with carbs. Runs aprox. $450.00 - 500.00 for a real pro to do it.

The distributor looks pretty new, new wires, ect. I have only had the car since last summer, so I assume someone would have done this. Maybe not. The carbs have virtually every vacuum plugged and/or linked but that is a great point to check out. Thanks.

[naro914]

Someone wiser than me told me once that 90% of carb issues are electrical...

I though he was crazy until I found that the "carb" problems we chased for months turned out to be the coil was cracked, and bad plug wires.

Point being, check all the ignition components and make sure it's timed correctly.

And yes, PMO carbs are wonderful well worth the $$ if you plan to drive it fairly often. We have PMO on Papa Smurf, and have had NO problems since we built it.

[ellisor3]

Someone wiser than me told me once that 90% of carb issues are electrical...

I though he was crazy until I found that the "carb" problems we chased for months turned out to be the coil was cracked, and bad plug wires.

Point being, check all the ignition components and make sure it's timed correctly.

And yes, PMO carbs are wonderful well worth the $$ if you plan to drive it fairly often. We have PMO on Papa Smurf, and have had NO problems since we built it.

Thanks for the advice, I guess in need to start with electrical and work forwards. By the way great article in Excellence. Glad to see him still running.

[naro914]

Thanks. Bob Chapman did a great article.
Huey is pretty much done now, except for a few oil leaks that have arisen this weekend - and not minor ones either, but easily fixed.

Just fyi, since we thought the problem was carbs, or engine, or... etc...just about anything except a coil ..... we ended up buying a whole new engine!! Once we put the 'old' engine back in another race car (the one I have for sale) it ran PERFECT - the only difference between the two cars was the coil and MSD box. Checked both, found the cracked coil. Would have saved a lot of aggrevation, time, money, etc. had we known. Oh well, now we have a really nice 2.7 in Huey! (IMG:style_emoticons/default/smile.gif)