Bike Carbs

Level 1 User Joined: 14 Apr 2004 Posts: 29

Since my RT SPI is really crap and I cant change the chip of the ECU (delco ECU, not siemens) I'm taking a look over carbs. well.. only have 200mm of engine bay clearence to fit carbs.
Knowing this, I'm gathering info about the use of 4 bike carbs on car engines.

Anyone has got any info about this? URL's, personal experience, have hear someone saying.. etc

A few questions passed my mind..

Why did weber design a HUGE DCOE carb if there is someone who designs them so small to fit bikes?
how small is the float chamber of a bike carb? will this affect fuel delivery to engine?
for a 1390cc car engine reving up to 6500rpm which is better? 36 or 39mm bike carb? (I think you cant change choques/venturis on bike carbs).

Hope that someone can help me with this.

Forum Moderator Joined: 16 Feb 2004 Posts: 1356

36 / 39 in my mind is to small mate...

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

39mm--why is this to small???

any bigger and not only will bottom end be shite (low gas velocity,crap atomisation, blah blah), but there will be a point of throttle opening beyond which there will be now change is gas flow. i.e if they are too big--there is only a throttle restriction upto a certain point, so u could go to say 75% open, but beyond this there is no increase in flow.

our race car (1.4 8v) uses 40mm throttle bodies, and they are spot on..........

wot (I mean what really) would u recomend then?????

bike carbs are smaller cos bikes need to be as light weight as poss. plus packaging is a lot more restricted.
DCOE's are not exactly modern day!! (but dont forget they are twins, so goin to be bigger than a single anyway)
wouldnt have thought fuel delivery will be a problem. think of the size of a float chamber on any 1.4-1.6, its not big as the total of the four on bike carbs......

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

36 or the 39 will be big enough.

Like Stan said, size isn't everything.

Also like Stan said the webers are in their late 40's. Cars were running them back in the 60's. Things have progressed far since then.

Bike carbs on cars can be good. The main problem is setting them up, not cos its complex etc its because a lot of rolling road operators have even less of a clue with bike carbs and getting different needles etc for bioke carbs is tricky unless theres a decent bike shop near you.

Anyway before delving into bike carbs etc whats actually been done to your engine?

I very much doubt its at its limit as is.

George (Soneji's) clio recieved headwork from me still runnign the stock ECU, airbox and cat the thing flew. It wasted my 2 litre saab and he kept up with clio 16V's. It used to get to 6krpm in 5th easily which was 120mph.

6500rpm is also a very low limit. I used to run mine to 8500rpm on the stock 100K+ bottom end. Now becuase I used a different head and its valves and springs, valve bounce now occurs at a low 7500rpm (on the 203k mile lump).

The engines are fine with high revs and my engine is a testament to their longevity if maintained well.

That was a problem with georges clio, the thing would start pulling really strongly around 4500rpm pulling harder than it would hit the limiter. The limiter was hit in all gears aside from 5th.

The headwork I done on his car wasn't as extensive as it could have been, there was more to be had. It was running stock valve seat angles and valves, there was more to come.

Also the exhaust and induction side could have been better.

the stock exhaust is a tad crap and the manifold leaves a lot of room for improvement.

Anyway enough of that. i would recomend you get the head seen to, match the manifolds as well (i forgot to add I did that as well) sort out the induction side of things then the exhaust and then see where to go.

The energy engines are good and can be made surprisingly quick. Start with the basics before adding carbs which are just going to need altered at a later date. if you do the other stuff you retain the injection which means nice starting, decetn fuel economy etc. Then when its limiting you get the carbs.

Level 1 User Joined: 14 Apr 2004 Posts: 29

I'm just looking into all possibilitys mate.
My RT is almost std. It has got the basic mods: decat, air filter.

since I know that the energy engine can be tuned to levels that would chase valvers, I will go with it instead of valver lump. Besides, spares and maintnance is cheaper. Smile

Been searching here and there and would say that 34mm or 36mm max.
Tomorrow I'm getting some tech manuals from honda, kawazaki and suzuki bikes. Hope to see whats best for a future mod.

For the first mods on the engine I'm going into all at once.
- 4-2-1 tubular ex manifold
- head work (with 3 angle valve cut seats)
- inlet manifold match
- SPI inlet shaft worked ( going to grind off some of the bolts ends and head; the spindle is going to be half with reduced and radiused; this will improve 10-12% of more flow... I hope )

On a latter day, I've already looked into some cams from catcams (www.catcams.be)

Chris, energy std valve springs can coupe up to what? 7500rpm and it starts to have valve float?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

the manifold where it goes from the TB drilled hole is very sharp, round it off.

Well the original springsd I had were fine to 8500rpm, I bottled out taking it any further. The springs in it now are from a later engines, the engine i got them from wasn't well looked after and I think it had overheated thus the springs had lost their temper.

but 7500 is a safe reliable redline.

Level 1 User Joined: 14 Apr 2004 Posts: 29

Got some service manuals from suzuki and honda. Usually their carbs are mounted on a 30 to 35degrees angle from floor. This is due to have the inlet mix going downstream so it can flow more? Or its because of fuel float chamber?

I think this carbs can be mounted on paralel to floor because bikes climb hills, "lay" to left and right and carbs still suply fuel to engine (they dont suffer from fuel scavage).

I hope that I explained my thoughts here. Some times I lack of english vocabulary Razz

Please feel free to comment since I need some hints on this subject.

Thanks

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

its for the float level. So you will need to tilt them up from the head.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

just wot (I mean what really) i was gonna say!

Retroholic Joined: 12 Feb 2004 Posts: 5685

Yeah yeah stan, me an all Wink

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

lol

Level 1 User Joined: 14 Apr 2004 Posts: 29

float level... oki. Smile