Caterham, Weber, Burp

[CraigH]

Morning.
I have a 98 Seven, 1600 Crossflow, Twin Webers. periodically, usually after aceleration, the engine will ignite/pass back through the Carb. I believe this to be a timing problem but I am not sure....can anyone give me an idea to confirm/diagnose this as the problem.....or give me an idea of what this might be. There are know timing mark indicators on the engine, but I plan to fool around with the timing a little this weekend to see if this might help. Any further assistance would be greatly appreciated.
Thanks
c

 

[DrEntropy]

Timing would be the first place to look. If you can (I know how tight things are "in there") it would be a "peace of mind" thing, to check how close the timing mark on the pulley is to actual TDC. A dial indicator is the best way, down thru #1 plug hole to determine it.

Some amount of this is to be expected if the timing advance is a bit further than 10~12 degrees static.

When you lift out of the throttle after acceleration there is still a residual amount of fuel in the runners and it can flash over to cause the "pop" thru the carbs.

Just curious: These are 40 DCOE's, right (as opposed to choked down 45's)?

 

[CraigH]

Thanks Doc
Yes they are DCOE 40's..........
It is difficult to work without timing marks.... but I will work through a hit and miss approach......
Thanks for the message on residual fuel that might be the problem....I had thought that could be a problem, but don;t fully understand how that fuel would ignite....
I dial indicator may be a good purchase.....
Thanks
c

 

[DrEntropy]

40's good. They ~may~ be a bit lean, but I doubt it. When you lean out the mix (by lifting) it's a bit more likely to flash, then create that "lean pop" backfire condition. "Spitting back" is what it's called. Keep an eye on the air cleaners: they can become gas laden and cause some VERY unpleasant things to happen if neglected. Best ones I've found are the individual "sock" foam type. Easiest to remove/clean/reinstall. "Uni-Filter" or something like that. Summit Racing has 'em.

 

[CraigH]

Spitting Back...... that describes the syndrome perfectly and yes you are correct..... it throws back thick nasty mucus on the bright Yellow wing through the K&N filter. The malady seems to occur only through one Cylinder but I don;t know this for sure. Any other possible remedies is greatly appreciated.....
thanks
Craig

 

[DrEntropy]

If it's only ONE hole, you may have a bent throttle shaft. Not unusual if someone not familiar with Webers fitted 'em and overtorqued the nut on the linkage... lemme guess: The hole spittin' back is #2?

/bcforum/images/%%GRAEMLIN_URL%%/smirk.gif

 

[CraigH]

Incredible...... I do believe it is the second hole.....
Hummmmmm...... If this is the issue.......what is the fix....
Surgery on Weber Carbs intimidates be a bit..I have the Braden book.....but was hoping to never have to dig into it.

Craig

 

[DrEntropy]

Got yere attention now?!?! Hmmm? /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

The only fix is a shaft replacement. I can't be CERTAIN that's the problem you have but I've seen it sooo many times it's the first place I check to rule it out.

A really Quick 'n Dirty way to check it is with a "UniSyn" or other manometer. At idle the twin throats should be hauling the same volume of air side-to-side for each carb. If one's higher than its mate, you've likely found a bent shaft.


...don't let this get around. It'd ruin my reputation as a shaman! /bcforum/images/%%GRAEMLIN_URL%%/smirk.gif

 

[CraigH]

I do have a German Made Synchrometer,,, is that what you are referencing.........??????

When I try to Sycn things up after pulling the carbs.... I have never had an equal reading on both holes on one of the carbs........I can;t remember whether it was the fore or aft carbs......but my guess is probably the same as yours....

I think I will do some reading tonight.

Appreciate the help......and will report back once we dig into the project......

FYI my son runs an anodizing business and we are "dressing up" the ALU in the engine compartment.....Rocker Cover, pedal cover...... etc......should be pretty nice.

Regards
Craig

 

[DrEntropy]

Good!! The spindle on the uneven one will be your culprit. First time I encounter'd this was in about '76. Just acquired my '65 Lotus Cortina and was setting it. Had owned an Elan for five years so knew the "regular" things to do, kept looking at all the ~wrong~ things. Spent a few HOURS trying to find why I couldn't get it RIGHT... but when on a lark I went throat-to-throat with a UniSyn it dawned... felt -stoopid- but had spares and redid it fairly quickly.
A garage full of pals had a fine laugh, tho. /bcforum/images/%%GRAEMLIN_URL%%/blush.gif

The anodizing sounds neat. Very classy! Have you ever seen the Weber poster with a "car-hop" girl? Left bottom photo is a DCOE with a black body and all the covers, air-horns and linkage plated gold...

That'd keep 'em guessin'! /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

 

[CraigH]

Ok...I pulled the carbs...... cleaned them up...etc.

Here is the approach I took to try to further verify the bent shaft theory...... see if you might concur.......

I took the carbs into the dark room and shone a light down the horn and look through the other end.... to see what light might escape around the seat of the throttle plate against the houseing...the only trace of light I could see in all four holes was......... from the second hole..... only a trace/sliver of light.... but still.... it is the only visible flaw I could see in all four....... so I assume this could be the the problem..... or a place to start..

That being said I have read up on shaft replacement.....look delicate but doable for this neophite...which leads me to the next question..... where does one get replacement parts for DCOE 40's.......

Appreciate the help
Craig

 

[DrEntropy]

I'll suggest Dave Bean Engineering (google it, it'll pop up) as a first try for replacements.

There's actually a probability you can't "see" the bend, as well: the blade slot in the shafts extends past the throats left and right. The tweak can be at the slot of the shaft outboard of the blade (and hidden in the shaft bore of the body) and so be near-invisible. It'll allow air past it but light doesn't 'bend' around through it. The only 'good' way to be certain is disassembly. Take your time, "read ahead" with the manuals. The units are metric throughout so no worry as to "Rudge" or other "funny" stuff. "Progress photos" are always a good idea too... for reassembly reference.

 

[RonMacPherson]

Have you done a "google" for Weber carburetors?
There's five or six that I have dealt with in the past. I would expect that Dave Bean's prices are going to be on the high side rather than dealing with a Weber importer.

 

[swift6]

Some of the bigger importers won't even talk to you unless your a shop. They don't all do retail.

 

[DrEntropy]

I ~had~ a number to the distributor in New England somewhere, along with a contact name... they'd only deal with shops. Can't find it now. Had to order some venturi chokes a while ago and paid retail for 'em due to my stupidity/disorganization. It's one of those "little things" forgotten in the chaos of shutting down a shop. bah.

 

[Grantura_MKI]

Try out Pierce Manifolds. They are located in California, but Mike may be able to help you out. Make sure that you fit the butterflies the right way round, before you split the fitting screws.
Cheers, David.

 

[DJThom]

Try Oliver Clubine at Britain West

(519) 756-1610
148 Pleasant Ridge,
Brantford, ON N3T 5L5

He's a veteren vintage racer and his company builds race engines for Formula V among others. He's got a nice Elite to boot, plus he's a nice guy.

I got all my weber parts from him. If not, Google Pierce Manifolds. No experience with them, but have seen their ads in various spots

 

[TypeRboy]

Just a quick note, and something to try.. I have had great success bending the throttle shaft straight again.. Haven't replaced one yet! You need to lock the shaft on one end ( with a wrench or vice grips with the shaft nut removed ) and apply force to the other side of the shaft again on the nut or on the actual shaft.. depending on which way you need to force it, one of the shaft nuts will want to undo, hence the vice grip on the actual shaft. This is done with the carbs in situ so that the shaft only twists and doesn't actually bend ( it's not bent really, it's twisted.. )

The shafts are quite soft ( give me Delorto's anytime ) and bend quite easily. You can pull the idle mixture screws and actually look down in there to see the alignment of the plates, but a unisyn works best as it is an absolute test for flow.. you can twist a little, start the car and flow test, repeat as necessary.

Try this first, as your new shaft is going to bend again over time anyway.. the springs in the carbs pulling against the linkage is enough to bend things.. I hate those shafts.

 

[Guest]

( give me Delorto's anytime )

I've just had a new bottom end built for my TC. Currently I'm still running the Dellortos but I'm having mixture problems. Do you have a source for emulsion tubes, etc?

 

[DrEntropy]

I've NO resource for Dellorto carbs, sorry.

...Make sure that you fit the butterflies the right way round, before you split the fitting screws.

Is there a story in there, David? Hmmm?