1.7 Carb Probs

[Subnet]

I have a 70, 914-4 1.7 converted to carbs. When I start it in the morning it will hesitate and sometimes back fire. Also, when I am driving in the mountains and going down hill it does the same thing. Crackles and pops.

Can anyone explain this? It is a Dual Webber setup 40IDF. I think the stock FI fuel pump is being used.

Any Help is greatly appreciated.

[nutzforporsche]

Now there are probably many people who will question my thoughts here. First I was under the impression that a different cam is needed in a 1.7L engine to run carbs. You will need to make sure that is done, the stock cam for F.I should not be used, ok for 2.0L though. If you are using the stock F.I pump it is way too much pressure for carbs and you really need a facet pump for carbs, that is another potential problem of getting too much gas to the carbs thus back firing. They are designed for only 4-6lbs without damaging something inside the carb. Hope this helps.
Steve

[Subnet]

I forgot to mention that the carbs have no chokes? not sure why the previous owner did this.

Any petucular brand or model for a faceted pump?

Thanks for the Help

[Dave at Pelican Parts]

I'm one of the people who will disagree with "nutz".

The stock cam for the 1.7 is in many cases absolutely identical to that of the stock 2.0. The ones that are different have very few and very small differences. You can run a stock cam with carbs, you just won't be getting the most out of the carb setup.

"Facet" is a brand of pump. It's cheap and noisy, and some people have had problems with them leaking after about a year. Holley supposedly makes a good pump that is available at many FLAPS (Friendly Local Auto Parts Stores).

I'm not sure if your cold-running problems are simply a fact of life with carbs, or if they indicate something wrong. I do know that none of the popular carbs for 914s have chokes or any provision for start-up.

(OK, the IDA [I think] has some provision for it, but I've never yet heard of any 914 with IDAs on it that have those extra parts installed. I don't even know if they actually make those extra parts.)

--DD

[mich914]

I have been running 40 IDF's on a 1.7 for 20+ years. My car is not a daily driver, so my solution may not please you much. when the weather gets below about 60 degrees or below, (I do live in Michigan), I let the enigne warm about a few minutes before driving. This corrects the cold start issues.

As to you other problem, backfiring at closed throttle, my experience is that (assuming the carb's were reasonably close to begin with), that this is almost always a timing/dwell issue. If you are running a 009, it is even more sensitive. It wouldn't hurt to check the valve gaps.

I have had the same facet fuel pump for 10+ years with no issues

dan

[DDS]

Stock fuel pump has much higher pressure than is required for carbs - I would guess that with an unregulated stock pump the the float bowls would just flood, so if it is running at all, the pressure must have been regulated to a more appropriate amount. ( If you haven't checked, I bet it ain't stock)

FWIW, Some Webers have cold start circuits that involve a cable actuated plunger valve that permits extra fuel to flow through a separate passage.
DCNFs and DCOEs and others have this. I think its the 'progressives' that may have chokes. (butterfly type air restrictors.)

I've also heard that those facet pumps aren't great and that your local FLAPS will have better options.

[mich914]

BTW, my 20 year old fuel pump is a Facet. Maybe they made 'em better back then

[Joe Ricard]

Time for my .02 cents on facet pumps. The sooner that noisy sucker dies the better. Of course me being withot ANY sound deading it is running neck and neck with the 2.0L motor. Just got back from a 45 minute blast around town. 44IDF's ran great for about 40 min. then just got all of a sudden crappy. After further review another idle jet plugged up. both main gas jet stacks shook themselves loose, one was like three turns. Car would flat fall on it's nose as soon as the main gas circuit kicked in (duh wonder why).
Oh yeah no ckokes either. Wait till I pull out of my driveway at 5 am tomorrow. I am sure I will hear about it from the Nieghbors. They have gotten to tolerate my 928 with cat bypass and Borla. He He.

[sweater914]

pressure is a big deal with webers, getting a fuel pressure regulator and putting in line to run between 2.0-2.5 will help, you can get them at local parts stores for about $25, if you have more problems try calling Pierce Manifolds at 1-408-842-6667, they eat, breath, sleep weber carbs

[Conrad W Peden]

The crackle and pop can also be a symptom of burnt valves or exhaust leak.

Before you tell me you dont have a leak...you have an aftermarket muffler right?(most carb conversions do) The note that most aftermarket mufflers ive heard can drown out the small leak it takes to produce this problem. The leak doesnt have to be big either, just a pin will do it.


good luck