I have Falthead in my dyno. Motor is mostly stock with cam from a frensh 3.9 Edelbrock heads and Edelbrock twin carb intake. Ignition is Magneto with 2° idle and 26° at 3500. Carbs are chinese repro Stromberg They idle fine but when get gently off idle they go lean when accelerating hard engine spinn fine up to 5000 and sound powerfull. I dont trust that chinese stuff and put on a set of rebuild Stromberg and they have much smoother idling but the same effect. When softly open the throttle they get lean an stumble. Is that typic for the Stromberg carbs? The problem is that the waterbrake get a load on motor in that range and it die when open the trottle with the water on. Is it wort to cange to the Holley carbs? Thanks
Those are not Stromberg's, Speedway 97's are not Stromberg's. The only real 97's being built new today are from England here www.stromberg-97.com ask for Clive. I have 3 of his on a blown flathead and they run out beautifully and have for years. It aint you, it's those knockoffs.
Have you contacted Max Musgrove, the Stromberg go to person ? madmax1946@comcast.net, or 1-801-583-6169.
Stumble off idle - accelerator pumps not working in carb (leather cups ****ged, pump rod missing in action etc). Easy to check - engine off, pump throttle and see if fuel is squirting down the carb throat. Cannot remember if the EE's have idle transition holes (suspect so) which may be coked up as an alternative. A mild vacuum leak can also behave like this. But to have the above happen on two sets of carbs would be unusual. Would make me suspect either the vacuum leak is not on the carbs (eg manifold connection for vac advance) or you have the timing set wrong (a little retarded). Cheers, Harv
Check the accelerator pump link that snaps onto the side of the throttle linkage. Look for excessive slop in the link connections. If the links are worn, your throttle ****erflys will start to open before the accelerator pump. This could be the cause for the engine to go lean right off idle.
here is a link to Toymakers thread from 2011 that has a lot of info on 97's that is a good read and informative FWIW Great Stromberg TECH Article | The H.A.M.B. (jalopyjournal.com)
Yes, a PCV can have a similar effect to a vacuum leak. It should be taking crankcase gases and putting them into the manifold. Crankcase gas can have a lot of air in it if the engine is fresh (little blowby). At low RPM, you have high manifold vacuum and the PCV valve is shut. As RPM increases, vacuum decreases. The PCV valve begins to open, letting crankcase gas into the manifold. If your PCV was leaking (jammed open) you would have lots of crankcase gas entering at idle. This is normally "fixed" by richening the idle mixture. Probably not your problem here. If the PCV is opening early, the engine is still on the idle circuit, the engine flow is low (so the PCV air makes a big difference) and your engine can go lean. The lean part makes the engine hesitate/stumble on acceleration. As the engine continues up the rev range, the main jets start working, overall flow is much higher, and the little PCV leak does not make much difference. The engine gains power and climbs nicely to WOT. An early opening PCV could be your problem. This one is easy to test for. Disconnect the PCV hose, and block off both ends of the hose temporarily by inserting a bolt into the end of the hose. Start the engine, and see if it still hesitates on acceleration. Note that with the PCV disconnected, you may get a little crankcase gas coming back through the breather. Cheers, Harv
All PCV Valves are not created equal. They are matched to the engine size and intake flow. I have always tried to match the engine size to the PCV Valve application.
When you say Chinese "97" are you talking about the cheapo knock off ones from ali express that can't be tuned for ****?
@Harv thank for good explain. In english I often miss the right words to describe how it works- But in the Stromberg are only 3 systems idle normal and full, there is no soft transition from one to other. Problem to test without PCV is that I install PCR on underside of manifold for nice look...... @chrisp I think they are such knock off china replic I got them together with a few other parts. I invest much time to get them running, but the idle is much nicer with the rebuild old ones. I get a batch of 15 France made Strombergs most 22.2 but few 24.6 and 1 1/32. there are all in good condition and I better invest my time in that. @saltracer219 the PCV valves have different flow? There are no equal at all?
I too buy all the 22.2 and 24.6 I can at swap meets (81 and 97 for the US) even if they are not that easy to come across they're not expensive as rebuildable cores, I even found a couple of Ford 94. The cheapest I got some was $25. I've seen those chinese knock off on Leboncoin (our Craigslist) floating around, I think some people try them out then and when they give up try selling them back cheap compared to a new Stomberg but still more expensive than on Aliexpress and way too expensive for what they are.
@Tow Truck Tom sorry for that but I think you understand my worst English better than my good german @chrisp Leboncoin is a good source, but often they want not send outside France I give a little more ignition advance and the stumble is much better now. Next problem is to limit ignition advance aon the magnetos
Sure,, I just thought your fingers were overworked, from too much tweaking. Like the Slingshot. Keep at it-( tweaking ), stay in touch.
Good news on fixing the stumble. Looks like a Vertex magneto. Modifying the magneto advance is more difficult... need to open the magneto and change advance plates. Cheers, Harv
Yes twin magnetos It was much work to get them syncronised The limiting plates must be changed, but not easy to get the right advance first time
The Jalopy Journal
