Dhla Help

[RO78IN]

Hi guys, running a pretty hot 3k, with twin dhla45s on it.

I know they are too big (plan is for 10,000+rpm) but these are the settings:

34mm chokes

135 mains

7772.7 emulsions

190 air correctors

55 idle set,

33 pump jet

 

Theres a big flat spot on jet change over, but the main problem is that one carby is running MASSIVELY rich bottom end, so much so that within 10ks driving, the plugs are black. All the jets seem to be the same, emullsions clean, floats the same. Is there something that I'm missing?

 

Thanks in advance.

Matt

[altezzaclub]

Unless you bought the jets new, swap all the jets just in case someone in the past drilled them. Swap the needle and seats over while you're at it. If the richness move to the second carb, swap stuff back one set at a time.

 

Check that the chokes are held firm in the throats, that can be a problem.

 

When you say the floats are the same, does that mean when you pop the tops off the fuel level in each carb is the same?? Especially if you do an ignition cut as the motor pulls really hard at 3000rpm. If one carb, (two chokes) are both too rich then fuel level is likely.

 

If it has a flat spot as the main jets take over, the idles might be too big. That 55 should run a 2L, but that's not the reason only one carb is rich.

[RO78IN]

HI Altezza;

I never rebuilt these carbies, but did change a few of the upfront settings to new jets (what i could purchase anyway...) Now that i think about it, the mis-behaving carby did look to have a little water damage inside. I might take her apart and hopefully i'll find a little air channel or something blocked. If that don't work, i will do as you suggest, swap everything and work backwards.

 

Thanks mate! :)

[altezzaclub]

Yeah, strip them both and clean them. Get a 10ml syringe without a needle from the chemist and push petrol through all the little drillings you can find, then hit them with an air gun if you have a compressor. Look out for non-return ball bearings in the pump jets, don't lose them.

 

After the episode with the mudwasp on the rally car Webers, make sure the hose and connections between the carbs are clean too.

[lexsmaz]

What is the carby balance like ? the carby that is running rich could be doing more work & with possibly the jetting being to rich then causes the fouling ? ..

[philbey]

First up, you must have them dynoed by someone who can tune them. Otherwise you just won't get the most out of them.

 

I would get a dellorto book and step through the carby sizing. First issue thou, your chokes are too big for a 3k. I run 40s with a 28mm choke on a 5k, I might go up to 32mm chokes at some point for more top end. Bigger chokes give grief because air velocity is too slow and doesn't pull fuel through nicely.

 

Your other specs don't sound too bad but I'd have to check.

 

What is the letter after the dhla45 stamp? If its a g or h then they're probably later units that don't have manual balance circuits.