Stromberg 175 CD2 carbs on a basically VW Bus 2 liter engine. New plugs and wires. Carbs were removed and cleaned; there is no needle adjustment screw at the bottom of the bowl. It has to be done via 1/8" allen screw down from the top after disassembly.
The problem is the engine won't exceed 2500 RPM. Compression is good. It has 1/2 tank of 91 octane ethanol free gas, going to top it off with AVGAS, 110 octane low lead, hope that helps.
Thoughts?
Have you double checked the ignition timing and plug wires for proper firing order?
In reply to 914Driver :
SU and stromberg are different carbs. They work differently The Stromberg uses a rubber diaphragm to do what SU does with a piston.
Guessing as to what the fuel mixture should be is impossible without a lot more information. What gas you use isn’t terribly important until we get a lot closer.
The first thing to check is the rubber diaphragm. Stromberg Carbs have always had a tendency to crack that rubber diaphragm. So replacing those should be your first move.
Fuel mixture on both SU’s and Strombergs use tapered needles. Each needle has a code stamped at the top. Usually a 2 letter code. That along with the chart will tell you how rich or lean the needle is.
Thanks. I haven't replaced the diaphragms but I did inspect them and saw nothing.
Far out, are you running without the air cleaner/s ?
Did that once with a 3 cyl. SAAB. It leaned out at higher rpm without the box.
In reply to 914Driver :
They crack usually at the bottom of the budge and the way I check them is get the hot water as hot as I can stand and then carefully fill them. If the bottom is wet then it’s time to replace them.
Next if the engine won’t rev and you are absolutely positive it’s not anything to do with ignition. Point gap set correctly, Timing isn’t off, good strong spark at each plug , correct heat range for the plugs,
Then figure out if it won’t rev because it’s too rich or too lean. Too rich will have black spark plugs
too lean it’s likely popping back through the carbs.
Let me know what needles you are using and I’ll look them up (if I can find my Stromberg needle guides )
Helped out someone with a VW engine problem this winter we thought was a carb issue, wouldn’t rev over a certain RPM, and tended to stumble and die if you tried to rev it higher. Turned out to be a bad coil, even though it was brand new.
I cannot count the number of times I've fixed carb problems with new ignition parts. Eueo cars, particularly
Now- has this thing ever run properly with the Strombergs? If so and it's quit running well, either the diaphragm is ruptured, fuel delivery is weak, or there are ignition problems.
If it's never run well, the spec of the needles could be a mile off.
I assumed if it had a diaphragm and sliding cylinder; anything other than a butterfly, it's an SU.
FrenchD, the plugs come out honey caramel color, at one time the plugs were a bit smokey but seem OK now.
IceRacer, it's not a Saab.
In reply to 914Driver :
Honey color is about right indicating at some point the fuel mixture was pretty good.
If you can look down into the base of the plug, where the porcelain meets the metal that will tell you the exact fuel mixture under power but what you are giving me is good enough.
Since you are using non-oxygenated fuel you should have similar mixture strength.
Assuming the gas is fresh and not stale pretty good chance the problem has nothing to do with carbs.
In reply to 914Driver :
I know it is not a SAAB but it is an engine. Just one of the odd things that happen. It leaned out.
Does the VW engine still use the rev limiting distributor rotor? Might be defective. Just a thought.
Many years of working on/with SU & Stromberg carburetors and I never experienced a symptom like that traced to them.
No distributor, magneto. It's brandy new.
Ok, that's enough. First, air cooled beetle engine. Then, a pair of Strombergs, finished with a magneto.
Fuelled with coal tar? Flintstone style granite tires?
Edit:. I see now it's in a plane, which is another entire level of lunacy. Too much prop, not enough horsepower. How much horsepower does the prop require? The engine is making a bunch less than that, or somebody put a cam in that raised the torque curve too high in the rpm range.
This problem seems very familiar to me. Like I've heard of another VW engined airplane that wouldn't rev. Unfortunately, I don't remember the fix. Hopefully, it'll come to me as this gets discussed (although we don't know that this has the same problem).
Does this have a PSRU or is it direct drive?
Has it ever run correctly?
Were the carbs rebuilt in an attempt at fixing the problem?
In reply to APEowner :
The previous thread where an airplane engine didn't rev, I remember people discussing the propeller size and pitch.
frenchyd said:In reply to 914Driver :
SU and stromberg are different carbs.
Sure are. FWIW I have always tossed any smogged Strombergs on cars I've owned and replaced them with older SUs which are easy to adjust. Bolt pattern is the same.
In reply to wspohn :
I do too but not because I object to Strombergs. Rather because I had hundreds of SU needles and no Stromberg needles.
In an airplane ! Carb icing ? You need to have a source of heat.
I remember one winter when the type 2's had a problem with the cold air that came in the vents.
Dan
Did you manage to get this sorted and if so, what was the issue?
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