High End Problems
Sunday, 02-Jul-2000 00:33:54
IM haveing trouble reving over 5800 rpm's, the motor kind of surges(accelerates the lets off, over and over). Im running 40 IDFs with the 28 mm venturis. Its on a 1915 with ported heads(40-35.5). I was thinking about running 32 mm venturis. Would this help solve the problem? Any other suggestions? Thanks
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Almost sounds like your running out of fuel, my first guess, is it happening in high gear or any. (n/t) (Muffler Mike) (02-Jul-2000 00:41:17)
Its happening in all gears, really bad in first, right when i go to slam it into second it does it, kinda like a rev limiter..thanks for helpin (n/t) (HotStreetvw)
Re: It could be the jetting,could the ignition system,it could be electrical..... E-Girl... (n/t) (02-Jul-2000 01:46:27)
Re:How `bout valve float? what cam,springs? ( Mark H) (02-Jul-2000 02:28:04)
What jets are you running, idle, main and air? air is the top end, when you say like a rev limiter, does it sound like as if you just pulled a plug lead off at those
revs? (n/t) (Greg Ward) (02-Jul-2000 05:12:43)
1) your vents are too small. 2) if it's happening at the same RPMS in all gears, it's jetting. If it's only in 3rd or 4th, you are running out of fuel. (John
Connolly) (02-Jul-2000 13:25:01)
I used the same engine with a progressive and turned over 7500, the problem only started when i added the dual webers, the air correction is stock, the mains
are 140s. I had vw paradise tune it, but i think i had better performance when i tuned them myself. anyways, thanks for your help (n/t) (HotStreetvw)
140s!?!?? Try 120 mains and see what happens. (n/t) (John Connolly) (02-Jul-2000 15:02:33)
maybe you could try advancing your timing by say 2 degrees, always cheeper than buying new jets, if this doesnt help, just set it back and try something else
(n/t) (Tony Z) (02-Jul-2000 15:49:46)
Are the 140's to rich? I know you cant always go by the book, but the weber tech manual says 1.45s so i just shot low. Would it run better with the 32 mm
vents and the 1.40 main jets? (n/t) (HotStreetvw) (02-Jul-2000 16:40:36)
You can do the math: Rule of Thumb for weber mains is 4.1 X vent size. That puts you at 115 for the 28s, and 130-135 for 32s! 140s are perfect if
you have a 34 vent! (John Connolly) (02-Jul-2000 17:14:44)
Try an air/fuel ratio gauge and see if you are rich, lean, or whatever with your jetting. (n/t) (Craig Merrow) (02-Jul-2000 20:15:47)
Sounds like weak ignition to me. Had a similar problem way back when I started hopping up mine..... (n/t) (Ohio Tom) (02-Jul-2000 22:58:36)
The ignition is new, coil, dist, ingintor, wires, cap, plugs, they were all just replace a few weeks ago, but remember, it didnt have this problem befor i added
the dual webers, it ran good with the progressive. (n/t) (HotStreetvw) (03-Jul-2000 01:35:52)
Go with the 120's as John C suggested, 140 in a 28mm vent is huge, I also have a 1914 with larger webers than yours and a 40mm vent.It likes
145-150mains so your definitely running too rich... (Greg Ward) (03-Jul-2000 02:32:00)
I have a set of 115's, the ones that came with the carbs. They guy at vw paradise told me it would require the 140's. I guess hes wrong! Should I try the
115's? would this be to lean? I was told that Leaner runs better, is that correct? And i was told leaner can cause the motor to blow, huh? So should i try the
115's? You guys are alot of help. I am learning alot. (n/t) (HotStreetvw) (03-Jul-2000 02:44:57)
Read those articles!!! but I don't see why you shouldn't try them at all because.. (Greg Ward) (03-Jul-2000 03:59:14)
Do they sell jet kits for webers with like all the jets(air, main, idle)? Are they really expensive? I've been paying 5 bucks a jet. (n/t) (HotStreetvw) (03-Jul-2000
I installed the 115's, the motor ran like crap. It didnt accelerate very well, it kind or had a flat spot or somthing. I put the 140's back in and it ran fine exept for the high rpm problem. Should i buy a set of 125's? Or just change the vents? (n/t) (HotStreetvw) (03-Jul-2000 17:44:21)
Deal with one issue at a time. I think the vents are too small. (John Connolly) (03-Jul-2000 18:51:59)
e:How `bout valve float? what cam,springs?
Sunday, 02-Jul-2000 02:28:04
Youll need dual springs for your set up. But it could be like the others said and be a week ignition or bad condencer. When you get it sorted out I would go with some 34mm vents. Thats what dellortos come with stock.
You can do the math: Rule of Thumb for weber mains is 4.1 X vent size. That puts you at 115 for the 28s, and 130-135 for 32s! 140s are perfect if you have a 34 vent!
Sunday, 02-Jul-2000 17:14:44
Instead of trusting the book, try it and see what happens! This is assuming your idles are close, and you will still have to dial in the air jets.
Go with the 120's as John C suggested, 140 in a 28mm vent is huge, I also have a 1914 with larger webers than yours and a 40mm vent.It likes 145-150mains so your definitely running too rich...
Monday, 03-Jul-2000 02:32:00
does it run fast and well up to the 5800? Cause to give us a number on the air correction would be good too.
If your ok to 5800 then the next step is airs, I'll bet they are really small like 135 or so which will make it even richer up the top end.
Why I ask if it sounds like a pulled plug lead after 5800 is because this is all I could think of to describe the sound.
I have just gone through this whole process just recently. John Connolly was the data source and my sounding board to get it right.
First thing (it doesn't take long) is go to the Aircooled.Net website and go to the Carb articles. There are 3. Open each one and print it, (don't just read)and then stick it in a folder. Once you've read them you'll have more of an idea of what you are feeling.
If you could run to 7500 with the old carb then I spose your springs are fine.
It takes a little time to get it right but it will be worth it. It is a pity you couln't go a little bigger on the carbs and vents.
Read those articles!!! but I don't see why you shouldn't try them at all because..
Monday, 03-Jul-2000 03:59:14
as JC suggested 115 is actually the "theoretical" best and thats why they actually came with them. I've found most weber carbies set up for a VW are very close "out of the box" depending on what size carby you've picked for what application (apart from wild combinations of heads and cams etc). I still say find out what the air correction is and while your at it you might as well get the number on the idle jet too.
You will rarely melt anything if you have forged 94 pistons, but you could kill a spark plug if its too lean. Hopefully your spark plugs are easy to get to. if they are (your lucky compared to me!) then run it at least up into 3rd gear somewhere that you can do that safely and also have room to stop and then turn off the engine immediately (no idling the engine).If you pull a plug, say no.2 and have a good look at it. If you did this now to your 5800 with the current jetting I reckon you'd see it as black as soot.
If it is browny/grey thats ok. If you look further up at the white of the porcelain and it has little brown spots then you are way too lean, this will also have been evident by popping and cracking at higher revs, which you should avoid doing for too long of course.
I have seen electrodes melt from the plug which is the extreme end of the scale so get those other numbers HotStreet!
Deal with one issue at a time. I think the vents are too small.
Monday, 03-Jul-2000 18:51:59
you can buy 32s for those carbs, but if you want bigger, you have to machine them larger. Once you decide on vent size, you can get a range of jets (I think you need 3 sizes of EACH jet (idle, main, air) to dial in the combination.
I would get 52.5, 55, 57.5 idle 32 vent 125, 130, 135 main 180, 200, 220 air
Monday, 17-Jul-2000 11:32:46
Just curious. I am close to getting my engine back in the car. I have spent many (I mean many) days and nights jetting both dual 42 DCNF's as well as a pair of 44 IDF's. I grew partial to the IDF's and will be using them again. I learned a lot on my jetting journey, but also became overwhelmed, by the number of changes I had to make to possibly overcome flat spots due to the possibility of restrictive exhaust ports, and/or too small of an exhaust system. Of the number of carb-tuners out there, I am just curious at what you would think would be the jets of choice (idle, main, and air) for this application. Thanks for your help.
78x90.5, engle 120 cam, 1.25 rockers, Berg P&P heads, 40x37.5, 1 5/8" exhaust, 8.2:1 CR, 93 octane fuel, dual 44IDF's, electric fuel pump (running 2.0 - 3.5 PSI), 009 dist with points conversion.
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we need to know your venturi size! (n/t) (John Connolly) (17-Jul-2000 11:38:47)
Venturi Size - oops, forgot - 36mm (from memory, the stock venturis as spec'd in the Weber Carb kits) (n/t) (Jim) (17-Jul-2000 11:44:23)
Try 55/57.5/60, 145, 200, F11 (n/t) (John Connolly) (17-Jul-2000 13:01:54)