Dellorto blues, I've reached my limit Options

[barefoot]

For several years after After I but it all back together the car's been running fine, had to clean one carb once and that worked fine. Now it's getting worse won't idle, it just dies after I let off the throttle. Runs strong at higher loads but very poor at idle & low load. I've cleaned the carbs enough that think I could do it blindfolded. I know the points dwell is OK and I haven't touched the advance. Using a heat gun i can measure header pipe temps just before muffler and one cylinder on each bank is way lower temperature than it's neighbor after holding the rpm's just above idle speed.
Think I'll pull the carbs off and do a compression check just to rule out one thing.
Can't even do a synchronize without a smooth idle.
Is there someone in our group who is Dell 40 expert so i can send carbs off to ???
I've prided myself as a competent mechanic but this has got me on the edge.
Not having fun anymore (IMG:style_emoticons/default/headbang.gif)

Barefoot

[Osnabruck914]

I run Dells on my 2.0L. Are you sure the O-rings behind the idle adjusters are present and seated properly? That's bit me in the a** quite a few times and produced similar symptoms. Worth checking.

Osnabruck914

[fixer34]

Not familiar with carbs on a -4, but something doesn't sound right here.
One cylinder exhaust on each side is lower temp? So it isn't firing all the time.
If there are 2 carbs, one for each side, I would think it highly unlikely that both would have the exact same symptoms. Sounds more like a spark/plug firing issue.
I would give the rotor, cap, and wires a good going over.

[cgnj]

@Barefoot I am a Dellorto fanboy. Here are my questions. What type of sync tool are you using snail or unisync? Do you have a center pull linkage, cable linkage, or a hexbar or similar? post pics of the linkage to the throttle lever.

What Is your idle speed and is it stable? If you idle is stable, pull you plug a plug wire and make sure the idle drops. replace it and then test each cylinder. Let us know. At stable idle, are all of the carb throats Kg/hour of air the same? How many air bypass screws are fully seated? When were the valves last adjusted? Do you know what cam is in the car?

[barefoot]

@Barefoot I am a Dellorto fanboy. Here are my questions. What type of sync tool are you using snail or unisync? Do you have a center pull linkage, cable linkage, or a hexbar or similar? post pics of the linkage to the throttle lever.

What Is your idle speed and is it stable? If you idle is stable, pull you plug a plug wire and make sure the idle drops. replace it and then test each cylinder. Let us know. At stable idle, are all of the carb throats Kg/hour of air the same? How many air bypass screws are fully seated? When were the valves last adjusted? Do you know what cam is in the car?

My idle speed isn't stable I have to keep slight throttle pressure to kept running, thats my big problem, so i can't attempt a sync (snail) I know air bypass screws are set properly and hex bar linkage, but know it's set evenly. i know o-rings on idle mixture screws are intact and are set to same turns as when it ran well. it has a WEB 494 cam and I just recently adjusted valves for it's 3000 mile check-up.

[cgnj]

@Barefoot I will PM my contact info to you and some initial questions and instructions. It will make the process faster and we won't be bumping this thread. I attached a picture that shows how I believe the linkage is oriented as you look into the engine bay from the driver side.

[Osnabruck914]

Another common culprit could be air leakage where the intake manifolds meet the block. Are those bolts tight? Are those gaskets in good shape? An air leak there and you'll never get things to adjust properly.

Osnabruck914

[Literati914]

I know a lot of guys would be against this.. but I was watching a 356 video the other day where the owner tried replacing his original Zenith carbs with chinese reproductions, and was pleasantly surprised at how good they were. Said his car had never idled as good as it was with the reproductions mounted (since he's owned it).. They were relatively cheap too.

Maybe they make reproduction Dellortos that you could use while eventually having your originals rebuilt? Just a thought.

[Osnabruck914]

I know a lot of guys would be against this.. but I was watching a 356 video the other day where the owner tried replacing his original Zenith carbs with chinese reproductions, and was pleasantly surprised at how good they were. Said his car had never idled as good as it was with the reproductions mounted (since he's owned it).. They were relatively cheap too.

Maybe they make reproduction Dellortos that you could use while eventually having your originals rebuilt? Just a thought.

I tried Chinese Weber knockoffs when I had my 356SC- biggest mistake I ever made. The build quality was horrendous. Essentially, pot metal garbage.

Osnabruck914

[rhodyguy]

Are the plugs wet? Have you checked plug wires for common resistance?

[cgnj]

@litertia914 Empi D 36,40,45. There were some reviews of the 40 and 45 on STF. As I recall the 40 casting was fine. The 45 casting the throttleplate couldn't cover the first progession port. They have been around for around 10 years.

[L-Jet914]

For several years after After I but it all back together the car's been running fine, had to clean one carb once and that worked fine. Now it's getting worse won't idle, it just dies after I let off the throttle. Runs strong at higher loads but very poor at idle & low load. I've cleaned the carbs enough that think I could do it blindfolded. I know the points dwell is OK and I haven't touched the advance. Using a heat gun i can measure header pipe temps just before muffler and one cylinder on each bank is way lower temperature than it's neighbor after holding the rpm's just above idle speed.
Think I'll pull the carbs off and do a compression check just to rule out one thing.
Can't even do a synchronize without a smooth idle.
Is there someone in our group who is Dell 40 expert so i can send carbs off to ???
I've prided myself as a competent mechanic but this has got me on the edge.
Not having fun anymore (IMG:style_emoticons/default/headbang.gif)

Barefoot

To respond to your wanting to do a compression check that will be 1/2 of the puzzle. I would also recommend a leak down test too to make sure the valves etc are sealing properly. In terms of the compression check I'm not sure what Porsche recommends warm vs cold and WOT (wide open throttle) during your test.

[infraredcalvin]

Not familiar with carbs on a -4, but something doesn't sound right here.
One cylinder exhaust on each side is lower temp? So it isn't firing all the time.
If there are 2 carbs, one for each side, I would think it highly unlikely that both would have the exact same symptoms. Sounds more like a spark/plug firing issue.
I would give the rotor, cap, and wires a good going over.

Simple things first, check for spark

[barefoot]

Update:
tried driving it just down the street and was running on only 2 cylinders. Checked header outlet temps & saw that rt side cylinders 3 & 4 very low temps. So pulled the carb & cleaned it once again, did compression ck & verified spark at those 2 plugs
145-150 comp. so good there. now it seems to be running fine although way too high idle speed (I'd been advancing idle speed just to keep it running)
So now will do a balance ck when my snail gauge arrives, then play with idle mixture to try to balance idle exhaust temps. Wish me luck

Barefoot

[Superhawk996]

Apparently I’ve got an edit / operator error problem (IMG:style_emoticons/default/headbang.gif)

[Superhawk996]

FWIW - I’ve had issues in the past that requires a piece of copper wire to be run through internal carb passages to open up some corrosion or dirt.

I know you’ve said you cleaned but just blowing air or carb clean may not do it in all cases.

Make sure you’re not leaking air in at throttle shafts via small shot of starting fluid around exterior - if leaking it will suck in and increase speed temporarily.

Don’t give up.

[Superhawk996]

Oops - duplicate (IMG:style_emoticons/default/sad.gif)

[porschetub]

Another common culprit could be air leakage where the intake manifolds meet the block. Are those bolts tight? Are those gaskets in good shape? An air leak there and you'll never get things to adjust properly.

Osnabruck914

(IMG:style_emoticons/default/agree.gif) that would explain why it will idle with a bit more tip end throttle,seen this before ,cheers.

[dr914@autoatlanta.com]

the most competent mechanic in the world cannot deal with dellorto carbs, real junk when they get old, can them and buy webers if you must have carbs, even the empi dual 40s are much better than the CRAP-D carbs

For several years after After I but it all back together the car's been running fine, had to clean one carb once and that worked fine. Now it's getting worse won't idle, it just dies after I let off the throttle. Runs strong at higher loads but very poor at idle & low load. I've cleaned the carbs enough that think I could do it blindfolded. I know the points dwell is OK and I haven't touched the advance. Using a heat gun i can measure header pipe temps just before muffler and one cylinder on each bank is way lower temperature than it's neighbor after holding the rpm's just above idle speed.
Think I'll pull the carbs off and do a compression check just to rule out one thing.
Can't even do a synchronize without a smooth idle.
Is there someone in our group who is Dell 40 expert so i can send carbs off to ???
I've prided myself as a competent mechanic but this has got me on the edge.
Not having fun anymore (IMG:style_emoticons/default/headbang.gif)

Barefoot