Spark plugs fouling in 1915 - have tried everything....

[Greg Ward]

No, I get you, I agree, I would think 125mains would be way too lean...

So can I ask what your Air correction jets are?

Cheers,

Greg

Would it if the engine doesn’t get any air?

Well every engine I've ever tuned in, which is a lot of "1915's" should never have to run anything less than a 135main jet in a 44IDF and nothing less than a 155main jet in a 48IDF.
Of course this means that the air is available in the usual way, if it can't get ANY air, then it can't run at all...

[Erlend / bug66]

No, I get you, I agree, I would think 125mains would be way too lean...

So can I ask what your Air correction jets are?

Cheers,

Greg

Would it if the engine doesn’t get any air?

Well every engine I've ever tuned in, which is a lot of "1915's" should never have to run anything less than a 135main jet in a 44IDF and nothing less than a 155main jet in a 48IDF.
Of course this means that the air is available in the usual way, if it can't get ANY air, then it can't run at all...

 Greg; I modified your post to make it easier for everyone to read cronologically.



What I ment was that an engine running in an enviroment with less available air, should need a smaller fuel jet?

The bus it is in only have ribbed vents on one side, so if the seal between engine and car is tight, the enigne will maybe have less available air to suck in => hence the small fuel jet.

[Greg Ward]

Right, well in that case I agree completely, it's simply how it works...

From the morning to the afternoon at the same racetrack I end up changing jets, all due to the changing air during the day and elevation. You probably have heard of Mt Panorama Bathurst in Australia.

So on a 1915 engine revving to 8000rpm, and 48IDF's I change from a 160main jet in the morning (lots of cold air) to a 155main jet in the afternoon (warmer air)...

It's just the 125mains that I have a problem with, in 30yrs of playing with Webers on VW engines, I've never had anything with the size carburettors and venturies that Jens has that would need to run with such small main jets... If they were 40IDF's with 28mm venturies I'd understand.

So what are all your jets Jens? and what was the A/F ratio on the dyno that ended up with this jetting?

Cheers,

Greg

[Erlend / bug66]

Right, well in that case I agree completely, it's simply how it works...

From the morning to the afternoon at the same racetrack I end up changing jets, all due to the changing air during the day and elevation. You probably have heard of Mt Panorama Bathurst in Australia.

So on a 1915 engine revving to 8000rpm, and 48IDF's I change from a 160main jet in the morning (lots of cold air) to a 155main jet in the afternoon (warmer air)...

It's just the 125mains that I have a problem with, in 30yrs of playing with Webers on VW engines, I've never had anything with the size carburettors and venturies that Jens has that would need to run with such small main jets... If they were 40IDF's with 28mm venturies I'd understand.

So what are all your jets Jens? and what was the A/F ratio on the dyno that ended up with this jetting?

Cheers,

Greg

They are 36mm vents.

AFAIK the engine has only been in an engine dyno, not dynoed in the car.

[Martin S.]

Oh its a splitty. You gotta do the 70's thing and slap the old side scoops and add some stickers to them...

https://bringatrailer.com/wp-content/uploads/2014/07/1967_Volkswagen_Bus_21_Window_Deluxe_For_Sale_resize.jpg

[Greg Ward]

I'll ask what all the jets are over again.

BTW I'm just trying to help.. as I love tuning Webers in, I have done it on VW's for 30+ years.

I'm just not near you or in your country, so I rely on some data to be able to help.

Cheers,

Greg

[Speed-demon]

Hi apprecciate all the help.

The engine sat in a car belonging to a friend of mine. It is now taken out of the car. I will revert to you when I get the chance of looking at the rest of the jets. I do not think the problem is related to "air choking" anymore, as the car was driven with the lid open the last time the plugs fouled. So it must be related to the carbs or ignition. But I still cannot understand how too small main jets can foul the plugs.... This has to be related to idle jets, idle screw adjustment, floats or needle valves. Or heat related problems in the carbs (boiling gasoline or needle valves getting stuck when they get hot?). Or ignition related. The prblem is that every time the plugs fouled, the engine had been driven for quite some time (30-90 minutes). So it is difficult to sort these things without mounted the engine in a car.

[Martin S.]

Try and get pics of the plugs for us please. 

[Jim Ratto]

Maybe the jets have been previously drilled larger than the size they were stamped.

Sorry, I didn't ask earlier, but how many turns out are your mixture screws (running IDF's, correct).
And probably doesn't matter with your current issue, but have you experimented with the idle-air-bleed adjustment (if you are running IDF) to see if you can improve and clean up the issue?

Good luck nailing this down. I hate my own problems like this.

Jim

[Martin S.]

These kind of problems are frustrating for sure. I have a permanent AF gauge on my car which I've found very helpful for not only tuning, but as an indicator when shit happens unexpectedly, like a hose falling off alerting me and letting me know like a 'check engine' light.
With the prices falling for AF gauge packages, would it be smart to have one to help nail down these issues as they arise? Or would it just add confusion.

[Greg Ward]

Maybe the jets have been previously drilled larger than the size they were stamped.

Jim

You may have just answered my questions on this Jim, I stopped drilling and or soldering up jets for this reason, got expensive to buy new sets, must have $1000 in the kit over the years, but at least I know exactly what I am dealing with at all times.

Also, to Martins point, I have a permanent Innovate meter in the racecar, and a CB one in the streetcar, no guessing and a real world dyno at your fingertips for the exact place and driving/weather environment you are in. Invaluable.

I too would like to know what the answer is eventually, the only time I was constantly fouling plugs in my engine was with a very large cam and the wrong heat range of spark plug, it would drown the spark and leave me hesitating all over the place, the only cure at the racetrack was to take the car out the gate and run it through the gears on the road (race car was driven to the track)... I would then attempt to get to the start line without constantly starting the car.

Talk about a hassle!
Please check back in when you have some more info, I'm know I'm not the only one interested in what you find.

Cheers,

Greg