engine and drivetrain Engine Bogs On Decelleration

[KFunk]

^call steve nelson at TEP

carter fuel pump makes the exact pressure 40dcoes require(no regulator)

I've used that one, and had the same result.  I think I must just be a tad more abusive than most people, or the carbs need re-jetted a bit.

[zinz]

Thanks for all responses!

 

I dove back into my Tuning Solex Carburetors book last night.  1.5lbs of fuel pressure is recommended... that is not very much, and easy to exceed.  I bought a Mr Gasket pressure regulator last night, didn't install it yet as I was busy messing with other things. The book also talks about solving percolation problems by adjusting fuel float levels... just like you guys have been recommending. Fortunately, this is an easy adjustment on these carbs and can be done in about 3 minutes from the top of the carb.

 

Hooked up the Carb Tune again and tried once again to tweak the idle (it has been inconsistent) Wellllll.... I sprayed carb cleaner around each carb to see if I have any vacuum leaks.  Crap... throttle shaft for #2 cylinder is leaky.  I was noticing how the rods of the Carb Tune would bounce around...except for #2.  It was always steady. 

 

So, here is another issue I have to sort out...  It's not horrible, yet.  It's really only keeping me from a consistent idle below 1000rpm.  I can live with that for a while.  Spark plug color hasn't shown a lean condition on #2, but I'll watch for it.  Worst case scenario I'll have to re-bush the carbs and install new shafts.  Right now I'm going to slap heavy grease around the suspect area and see how the engine reacts.  Certainly not a permanent repair, but I think it might show me how bad my problem really is...

 

As for the fuel level/over pressure... I will address that over the weekend with fuel float adjustments and pressure regulator install.

 

Thanks again for all the advice, I'll let you know how the repairs go.  I want this baby running tip-top for Mid Am !!

[zinz]

Austin was blessed with perfect weather this weekend and I was able to make multiple adjustments and test-runs yesterday and today.

I was able to adjust the float levels and found it doesn't take much to make a big difference! First adjustment showed almost no stumbling problem after hard deceleration but was lean under load at high rpm. I simply backed off that initial adjustment till the car didn't run lean. At that point, the stumbling after deceleration was not gone, but noticeably better. I never did install the regulator.

Another part of the solution involved a quick-fix to the worn throttle shafts. They must not be worn very much but getting a consistent idle has been frustrating. I simply glopped axle grease on the ends of the throttle shafts. My thought was that the vacuum would pull the grease into the gap and "seal" them. I actually saw improvement. The Carb Tune was much steadier and the idle was smoother.

I know this wont be a permanent solution, but it's waaayyyy cheaper than sending them of to be re-bushed... We'll see how long it lasts. (and see if that grease causes combustion issues) There's a 5 speed swap planned this year, I may send the carbs off during that time.

Thanks to everyone who helped me sort this out.

Ed Z

[LarsAlpina]

Ed,

 

first I don´t see any Solex DDHT on your car (and Alpina did not use those either). DDHTs were the ones with the cold start device druffgebabbt on the side like e.g. used in Volkswagen K70. Take another look on the Ruddies site maybe.

 

You do have Solex 40DDH and those are the ones Alpina switched to in about 1973 or 1974 after they had before used Webers. No need here to explain the reasons why they did that.

 

Question: Do you have that Solex brochure on the DDHs (german language though)? If not do you want me to send you a pdf-scan via PM?

 

 

As already mentioned several times on the FAQ dual sidedrafts need to be jetted and tuned 100% accurately according to the surroundings they´re used in. Cam custom or stock, exhaust custom or stock, air filter used or not, etc. Let me give you an example:

 

These are the original jettings Alpina used on their engines. They used the 40DDHs only wiith their A1 kit for stock 2Liter engine, A2 kit with 300 degree cam (and some other work done) was already equipped with 45DDHs. 

 

 

What I marked red is for their first style kit when the still used the (typical for older Alpinas) stock TI can with the big NK 4-door filters. This:

 

 

What I marked green is for the later style kit when they had their own triangular air collector ready. This:

 

 

Now have a look at the differences in jetting with just changing the air filter system - engines stayed the same bone stock as before! I think that makes visible how important it is to get each and every car on dyno if you put on dual carbs to have it individually jetted under load (or you have AFR control installed and can check and rejet yourself on test-drives).

 

Note: Green marked data says Solex ADDHE. The only changes on those compared to DDHs were the housings to be made from aluminium and no longer zinc and some bearings added on the throttle shafts. Rest is perfectly identical to earlier DDHs as this original Pierburg document proves:

 

 

Concerning your idle problem maybe think of limiting the advance range of your dizzy a bit on the lower end. With non-stock cams and dual sidedrafts you may have the advance already set into operation while you´re turning idle screws on the carbs. That isn´t very helpful.

 

Best regards, Lars.

 

 

[LarsAlpina]

As for the jetting, Mike... Alpina used these carbs in aftermarket applications.  I found several references with their specs. http://translate.google.com/translate?hl=en&sl=de&u=http://www.02-club.de/technik/solex.htm&prev=/search%3Fq%3Dsolex%2Bddh%26hl%3Den%26lr%3D%26rls%3DGGLC,GGLC:1969-53,GGLC:en

 

BTW: Karl-Heinz (the guy that wrote most of the text on the German website you linked to) is really great on those DDHs. Besides other sources I`ve learnt a lot from him some years ago talking to him in person and on the phone.

 

Regards, Lars.

[zinz]

Lars,

You are a treasure trove of information... I am very thankful for all this information.

Both you and Juergen Ruddies said the same thing about my carbs not being DDHTs... but they are most clearly marked DDHT.

Drawings on the Ruddies site show this carb with the starter disk on the top.

I will try to absorb all this new information. The carbs are running fairly well and I found that adjusting float level makes a noted difference. I have been playing with several adjustments. The tune is very close. A wide band O2 sensor would very certainly help.

My timing is set at 25 degrees at 2200 right now. This gives good power and decent idle.

Let me chew on this new info and I'll get back to you with another update.

Thanks again for all the original tech data!!

Ed Z

[zinz]

I thought I'd better finalize this thread...

 

My setup is running VERY well now. Idles beautifully at 950-1000rpm, no hesitation from idle, through progression, to redline. There is only the tiniest dead-spot at 3400rpm when driving steady-state.  It's practically imperceptible...except to the OCD driver

 

So what fixed my problems? Several gremlins worked in tandem against me, but they have been exorcised.

 

Firstly, getting the fuel level finely adjusted helped a lot.  I was impressed how even an 1/8 of a turn would make a notable difference. Of course this adjustment must be duplicated from one carb to another.

 

Secondly, ignition... During my problem I was using an original, un-rebuilt, Ti distributer with points.  I went to a Hot Spark igniter and it helped, but not entirely. Then... I put in an Ireland Tii dizzy I had laying around, with the same Hot Spark igniter. All my poor idling and low speed stumble vanished.... obviously, the old Ti dizzy had loose springs and was not advancing properly (just as Lars had pointed out!)

 

LASTLY... out of left field... my brake booster had apparently been slowly failing and was causing a small vacuum leak during braking (remember the original problem?? stumbling after acceleration...during braking?) Yep, it would idle just fine when the brake wasn't applied, but step on the brake and it would flutter.  When I replaced the booster two weeks ago after it failed completely, the idle was PERFECT.

 

Sooooo... I now have a properly advancing distributer (albeit for Tii specs), a well sealed vacuum system and properly adjusted fuel levels, resulting in a car that starts with just a touch of the key, idles calmly and ROARS thru the midrange....just ask anyone who behind me during the drives at Mid America last weekend

 

Yep, this car is running very well, indeed.  Thanks to everyone who contributed advice to solve my problems!

 

Ed Z

[ray_]

I can attest this is a very fun car!

 

Cheers,

[zinz]

If my car is "very fun" then Ray's car is a maniacal beast. I will have a built, 2.5 liter S14 someday...wicked, wicked power