14 replies to this topic

[Danner1517]

Hi, looking for some help with old race engine. 1293 with 649 cam all the race things. It has weber DCOE carb. I've pretty much gone through the whole thing and it just won't run quite right. Getting a bit of miss firing but the worst part is when I rev it up to 4 of 5k the rpm will hang up there for way to long and slowly come back. I've checked for vacuum leaks extremely thoroughly, played with float heights you name it.
Obviously missing something. Any thoughts on the rpm hang up. And I can see in the carbs from the car the butterfly's are closed up and she still revs to the moon.
I've been working on engines along time but the mini and weber are new to me.
Thanks for any help.

[andyapanel]

I never put a Weber on a mini, but I did have one on a kit car which was prone to misfiring. It turned out to be an air bleed screw which managed to accumulate tiny amounts of gunk, despite the filter.
I hope it’s an easy fix.

[PoolGuy]

It’ll be an air ‘leak’, engines can’t run without it. 

[Avtovaz]

i dont know much about those carbs, but it could be something like its leaking fuel inside. Best thing to do is take it off, and watch this vid ill link that Andy Jones did which will tell you everything you need to know about it.

 

CLICK HERE

 

 

hth

[Earwax]

Absolutely check for airleaks - the weberDCOE45 prefers the soft mount kits - and I like the weber genuine but other products seem to work fine ( check rubber rings and dont over tighten

 

If an older carb I would take out the needle valve and give everything a good carb cleaner.,(probably done already)

Also check that the pump jets have the tiny washers/alum - for seating

 

I would also check that the Aux venturis 

 a( are pointing in the correct orientation  ( not in backwards and fuel hole matches flow 

b) aren't wobbling around - either locktab or wired into place

 

and regarding floats - the older brass ones can develop cracks on the supports -so the float discs wobble - not the tang - the arms that supports the weight of the float- so the float height wobbles a bit

 

and finally  ( My best guess for the hang up in revs) - inside the plate - ( not sure if called inspection plate or blanking plate - but after you lift the top cover away there is centred rectangle with a cover and inside is(or can be ) a small spring that helps the spindle to return --- these come off and can get jammed normally at high revs  --- lots of racers remove these because of this issue ( and you have to have 2 external throttle return springs in our race safety specification over here)

 

NOTE NOTE  Be careful if trying to take one out or put one in - i highly recommend eyewear -it is fiddly down at the bottom and twanging springs are common.. 

[nicklouse]

Old fuel in the carb can gum everything up.

 

Strip and clean the carb. Replace Theo rings and thackary washers if they have been over tightened. Or the rubbers that are used instead of the thackary washers.

[sonikk4]

Did you build this engine or buy as is??

How is the carb mounted to the manifold, is it the old type of double O ring sitting in a plastic receptacle or are they Misab plates??
Have the nuts been over tightened ie the spring washers fully compressed?? Speaking from experience here with twin 45’s on my old RS, if you have the old type of mount ie the plastic receptacle with a O ring either side, these had a habit of being over tightened the O rings would displace. I had all sorts of issues with these ( my fault with over tightening the nuts) and one was the idle was all over the show plus stupid things at speed as well. Turned out when I took the carbs off I could see the O ring had started to squeeze out causing all of my issues.

A set of Misab plates later jobs a good un plus I made sure I just nipped up the nuts so they were just starting to grip on the spring washers.

[Danner1517]

Hi all thanks for the replies.
So I didn't built the engine, bought as is, it was rebuilt then sat for years. I have cleaned the carb, twice now, it has the plastic plates with 2 o rings, I have misabs ordered, I have checked for vacuum leaks withe the old breakclean spray trick, found nothing, but that was also at idle so maybe I need have over tightened, wouldn't have thought that a thing. I'll try all your advice and get back. Thanks for helping.

[sonscar]

Block off the carbs cutting off the air should stop it.Steve..

[Danner1517]

Sonscar, please elaborate..

[Lplus]

Hi, looking for some help with old race engine. 1293 with 649 cam all the race things. It has weber DCOE carb. I've pretty much gone through the whole thing and it just won't run quite right. Getting a bit of miss firing but the worst part is when I rev it up to 4 of 5k the rpm will hang up there for way to long and slowly come back. I've checked for vacuum leaks extremely thoroughly, played with float heights you name it.
Obviously missing something. Any thoughts on the rpm hang up. And I can see in the carbs from the car the butterfly's are closed up and she still revs to the moon.
I've been working on engines along time but the mini and weber are new to me.
Thanks for any help.

Presumably by "the butterflys are closed up" you mean the linkages appear to be on the idle stops.  That doesn't guarantee the throttles are closed. Are the butterfly plate screws loose?  Are the butterflies centralised in the carb bores?

[Gaz66]

I had a similar problem many years ago with a Weber.
It turned out to be a manifold o ring that had been partially sucked in.
Might be worth whipping the carb off and checking they are all seated properly.

[sonscar]

Put your hand 0ver the carb intakes.the engine should stop almost straight away.if it does not you have an airleak.are all the hoses connected or blanked off?Steve..

[Danner1517]

Sonscar, I gotcha now, I'll be wrenching tonight, I'll give it a go.

Edited by Danner1517, 21 August 2024 - 10:46 PM.

[Danner1517]

Well big thanks to everyone who shared advice, chock it up to learning, I had a shoddy point to dizzy wire combine that for a poor idle and I was turning idle screw way to far to compensate "I think" so the butterfly was opening into the progression holes, causeing all my issues. Positive is I can now take apart a weber in my sleep.
Should be autocrossing the old girl tomorrow night. Phew.