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Weber vs bike carbs
ttalps2000 - 6/11/18 at 04:51 PM

I am currently running 40mm dcoe webers on a 1800 zetec with fast road cams producing 160hp. I am finding the webers do not stay in tune for very long, are a right bugger to balance successfully! Drivability is not too bad and all was setup on rolling road.

I do have some GSXR 1000 throttle bodies, however i have no management system and tbh dont really have a 1k budget to go and buy OMEX etc to run them. much better are the bike carbs over the webers? Get similar performance to the throttle bodies? Thinking of a DanST kit

I run Megajolt ignition management which i am more than happy with.


cliftyhanger - 6/11/18 at 05:25 PM

What is going out of tune? Mixture shouldn't need altering, and if you get hold of a morgan carbtune balance is dead simple.
In fact bike carbs will be just as hard to balance. And need am initial rolling road setup to get correct.

If you have some ITB's already, something like microsquirt is not going to be 1K. Maybe by the time you get an inlet, a wideband, fuel pump setup etc. But the bike carb setup is a few hundred quid. And won't be as efficient as injection. Power difference is small.

mikeb - 6/11/18 at 06:20 PM

I've had zx6r carbs on my 1.8 cvh, this was my IVA set up and did 400 miles on it, no issues. I put some bigger jets in (there's plenty of recommendations on what jets to use), adjusted the needle heights until the plugs were the right colour and didn't touch it again.
I'm now just putting a 2.0 zetec in, if I get a chance I'll get RR session but fairly happy I can get it about right. I didn't balance mine but didn't notice any problems. Bike carb seem ok, only problem is when you leave fuel in them for over a month.


SPYDER - 6/11/18 at 08:03 PM

Hi there. I would stick with the Webers until I could afford the move to injection.
As stated above, Microsquirt would be fine. You might probably be able to keep your filters. I did.
You will have the Webers to sell, as well as the Megajolt and a manifold. That will offset the cost.
Bike carbs won't give you what you are looking for.
If the cams would fit in a 2 litre I would be doing that at the same time.

ttalps2000 - 6/11/18 at 08:37 PM

ok, not as i thought then!

The balance keeps going out on the carbs, despite how many times i adjust them. I have a carb syncer too. Mixture doesnt change at all as its all fixed.

Good point about microsquirt and offsetting the cost. There is speeduino too, but unsure on that at the moment.

2L wont be going in, spent enough on the car as it is lol. The 1.8 seems revvy enough and produces decent power, so im quite happy at the moment!

cliftyhanger - 6/11/18 at 08:47 PM

The morgan carbtune does all 4 at once. So easy to adjust everything,and shows how adjusting one affects the others.

It is linkages going out?

mcerd1 - 6/11/18 at 09:08 PM

Originally posted by cliftyhanger
The morgan carbtune does all 4 at once. So easy to adjust everything,and shows how adjusting one affects the others.

^^ or make a 4 way one the locost way cheap from some plastic pipe and coloured water (not quite as neat, but much, much cheaper )

ideas linky

steve m - 6/11/18 at 09:10 PM

I also had a pair of matched 40's on my 1700 xflow, after two years of having to rebalance them on a weekly basis,
I gave up and stuck them on fleabay, got 1050 for them, as they were original 1960's webers, not the modern recreatione
I also had EVERY jet x4 ever made for them, and that is why they went for the price

I now run a 28/36Dcd now, and love it, down on power slightly, but fuel economy is good, and engine tractability is from
1000 to 7500, not like the webers 4,5k to 6


rusty nuts - 7/11/18 at 07:45 AM

I have bike TBs on my Xflow, I check the balance once a year using a set of vacuum gauges but as yet I haven't had them go out

ttalps2000 - 7/11/18 at 08:45 AM

as per steve m's comments, they go out of balance very easily! I have new linkages too to try and resolve the issue and is still the same. new seals, buts, washers etc too!

Lower down the rev range it is not too bad, but they come into their own when flat out. Would bike carbs be better low down too?

Going to TB's is not just an ecu, its all the sensors, wide band lambda etc too, quickly adds up!

JeffHs - 8/11/18 at 11:14 AM

I've got twin 40s on a 1600 Pinto with fast road cam. Pulls like a train in top gear from 1000 rpm and revs up to 6.6 with no hesitation anywhere in the range. Having said that it's taken me years to get them right. I bought a Webcon flow meter and found carbs way out and individual chokes on 1 carb were out due to a bent shaft. Much cleaning and fettling later, I made the biggest improvement last summer by tightening everything on the linkages, Weber advise that the spindle nuts should be just over finger tight but since I've boned mine up it's fixed most of the issues.

ttalps2000 - 8/11/18 at 01:32 PM

Tried tightning all the mechanism up and made things worst as it started to bind, so went back to the weber guides! What Webcon dont give you is how to adjust the mechanism correctly. All i have is 1 screw on the link between the 2 carbs and the idle setting screw, thats it! So unless im missing somthing, i balance them out with the link screw and then set the idle and re-check again. Its a right faff but get there eventually!

David Jenkins - 8/11/18 at 03:04 PM

The downside to bike carbs comes into play if you want to get them professionally tuned: most tuners will happily tune Webers, but many aren't keen to do bike carbs - too time-consuming as all adjustments have to be done 4 times, and stuff like jets and needles may not be easily available.

There are good tuners around, but you may well have to travel some way to get to them.