Dellorto jet sizes

[rusty1962]

Hi Guys.

In France......

Bus goes great on motorways towing Puck but slows uphill.

On little roads if I encounter a really steep hill, with or without caravan, bus struggles to get up it.

I think it's a fuel issue.

Yesterday I tried 98 octane but that resulted in lots of backfiring on overrun, when I lifted my foot going downhill etc.

Back on 95 now. Backfire gone.

Tickover has become a bit erratic when cold.

Engine generally running lovely but it's this lack of power up a steep hill that's the problem.

Engine temp is always 180/190.

I've taken a jet out and I'm running 122

Ideas chaps?

Steve

[Bren Ralls]

It’s been fine up till now Steve so just check the idler & main jets are clear.

[flatbeat]

What size engine is it ? Most buses pulling a caravan will slow going up hill. A lot of buses towing nothing at all will slow uphill.
You'd need a good strong 2ltr + engine to not be affected towing up hill and even then......
Check none of your exhaust gaskets are blowing...could well explain erratic tickover and backfiring (common reason).

[rusty1962]

Bus ran really well all week and we're home now. Engine starting to loosen up a bit I feel.

I'd expect it to slow up the long French (or English) hills on the motorways.

So the issue is......when I suddenly turn a corner on a small French road through a lovely vineyard area and am suddenly confronted with a bloody steep hill. Change down and floor it but the Jill's so steep the bus won't pull up it (No caravan) change down into first and the bus virtually comes to a standstill. After what seems an eternity struggling it gradually picks up and once going is away.

I ordered 118 jets from Eurocarb (currently122) and have installed them thinking it may have too much fuel going in or too rich a mixture - remember it was backfiring a lot when I tried 98....no backfiring at all on 95.

I need a carb specialist.. ...anyone ??

[flatbeat]

You need to know what size Venturis you've got to determine what size jets are needed. If you can see what size vents (not easy when carbs are fitted in a bus)then if you tell me the engine spec I'll let you know what size idles and mains are needed.

Nige

[rusty1962]

You need to know what size Venturis you've got to determine what size jets are needed. If you can see what size vents (not easy when carbs are fitted in a bus)then if you tell me the engine spec I'll let you know what size idles and mains are needed.

Nige

OK thanks Nige.

I now worked out what the venturi is.............

Is it possible to see the size without dismantling the carb?

TA

Steve

[flatbeat]

Yes if you take off the air filter and filter base and look down into one of the chokes you should be able to see the Venturi...it narrows the choke so it's that bit you're looking for. Shine a torch down the choke and hopefully you should be able to see a small number on one side of the Venturi. If they were anywhere near correct I'd expect them to have 30mm vents going by the 122 mains. Are they 40's or 36's ?
If you've got 30mm vents the 118 mains is gonna be too small. It may seem to run ok but it will be lean and run hot...not good!

[rusty1962]

They're 40s

[rusty1962]

So....DRLA 40s. Centuries are 30s. I've put back the 122 mains as I found some loose nuts on exhaust....not very loose though but Ive nipped them all up now.

According to charts I've found DRLA 40s should have 34 venturis and bigger main jets.....

[flatbeat]

No.....DRLA's should have whatever vents, jets etc suit the application. There is no 'should have'
You haven't said what size engine or what size idle jets you have.
With a 30 vent 122 mains should be ok and 58-60 idle jets....for a mild engine. Pump jets are prob 33 if still factory...usually ok unless big motor and other stuff.
You'll find tightening up the exhaust nuts will have a big effect on the back firing. Loose exhaust makes the engine run hot too. Nearly always gets overlooked and carbs get blamed every time
If the nuts were loose then the gaskets will almost certainly be burned and need replacing. You're wasting your time if they're not sealing properly.
Idle jets are the ones just in front of the mains....but they don't stick up...they're flush with the top.

[rusty1962]

OK thanks.
The backfiring only occurred when I put in 98 petrol. It hadn't happened before and happened less and less as I diluted the mix back to 95. Hasn't happened since.

Exhaust nuts weren't really loose but I was able to tighten most of them a little. I couldn't see signs of blowing. Having said that engine sounds different now

I'll check the idle jets and post back when I get a moment .

The trouble is we have no steep hill where we live so testing is difficult.....

Thanks for your help

Steve

[BJ1]

If the bus is bogging as you describe, then it could be that one or more of the idle jets is blocked. First renew all fuel lines as blocking is usually caused by ethanol in fuel rotting the lining of traditional Chinese fuel hose (often says R9 on the side but is fake). Check your tank and in line filters and then take all the idles out and check that they are clear. Chances are that the engine will run lots better but may idle much faster as the carbs have been tuned with blocked jets.

[rusty1962]

If the bus is bogging as you describe, then it could be that one or more of the idle jets is blocked. First renew all fuel lines as blocking is usually caused by ethanol in fuel rotting the lining of traditional Chinese fuel hose (often says R9 on the side but is fake). Check your tank and in line filters and then take all the idles out and check that they are clear. Chances are that the engine will run lots better but may idle much faster as the carbs have been tuned with blocked jets.

"Bogging" is a good word and accurately describes my symptoms........just like it's got stuck in a bog and is struggling to pull itself out.

I'll take out the idle jets and have a look at them later and will also report on the size.

Thanks, I'm slowly learning about carbs