VOLVO PENTA AQ170b TUNING PROBLEMS ??

[chiswick pride]

Hi
After three long years my wooden runabout project is finally at its end!
But we are having major troubles trying to get the 6cyl running well for 10mins or longer before it runs rough & start to cut out?
at the start we thought it was electrical so got new points,condenser & coil.
set the timing ,went out to test.ten minutes later same problem
thought maybe fuel starvation so checked manual fuel pump but had perfect 3.2psi pressure & flow test.
then noticed it looked like one of the sloex triple carbs was flooding out onto top plate,so got 3 new needle valves & check over carbs for blockages & cleaned.got them manually set set up by old volvo mechanic & ran well with water muffs on dry land for 1/2 hour.
took out for next test & STILL does the BL***Y same!
have noticed the plug which were cleaned before are now black & wet after only this 10-15 min test.
Can anyone help? is it still fuel carb problem OR electrical(weak spark not using up all the fuel in cylinder?) Have noticed it running NGK BP7HS & not BP6HS as shown in some sites would this be enough difference to cause this problem?
thanks for any help

 

[Bondo]

Re: VOLVO PENTA AQ170b TUNING PROBLEMS ??

have noticed the plug which were cleaned before are now black & wet after only this 10-15 min test.
Can anyone help? is it still fuel carb problem

Yes...

 

[PiratePast40]

Re: VOLVO PENTA AQ170b TUNING PROBLEMS ??

Here's the link to the fuel system checks: http://forums.iboats.com/showthread.php?t=283269

Sounds suspiciously like a fuel starvation problem so clean fuel filters and hooking up to an external tank might be an appropriate test to perform out on the water and under load. It's a process of elimination - just need to keep going.

Those carbs are relatively simple but not sure what you meant when you say you cleaned them but only replaced the needle valves. Disassembly and an overnight soaking and a complete cleaning of all the passages sounds more in order. Having 3 carbs certainly adds cost to rebuilding but I don't see any way around it.

As far a kits - it's allmost impossible to find the OEM carb kits any more. Some of the Volvo dealers are now substituting the Seloc as substitutes.

Compression test may also be in order.

 

[chiswick pride]

Re: VOLVO PENTA AQ170b TUNING PROBLEMS ??

Hi
So far have taken main jets ,idle jets,idle screws ,accelerator pumps of & cleaned thouroughly(all seemed clean with no blockages or sediment found) & replaced needle valves (possible flooding on rear carburetor,but seemed to close off manually & no leaks in floats)
carbs were balanced & when checked have correct amount in fuel bowls.
Would the plugs be black & wet after only 1/2 idle if it was fuel starvation??
I have done a warm compression test & reads;170,160,170,160,155,165. have not done a wet test(ie.oil down bores) would that make a difference as these readings seem OK?

 

[PiratePast40]

Re: VOLVO PENTA AQ170b TUNING PROBLEMS ??

Compression for that engine is listed at 170-200 so your'e at the low end of the range. You might want to check for contaminants in the fuel, fresh filter, that the vent is unplugged, and that the pickup line isn't geting plugged. A test run with an auiliary tank hooked up just before the fuel pump would be a good way to test that part of the system.

Syncing the carbs is absolutely a good idea but it only affects the idle circuit. I don't know how you can be sure that all the internal passages in the carb as well as the inlet screen are clear but that's your call. You can look at the fuel standpipes at around 2000 rpm and above. There are 4 holes in each of those little tubes and you should see 4 good streams of fuel coming out of those standpipes and into the venturi.

But again, there are several thngs you should be checking. The carbs are one of them but a good clean supply of fuel is another. It could be that you have debris in the tank that plugs the pickup tube after awhile. It could be that the fuel tank vent is partially plugged and starts affecting fuel flow after a few minutes at power. It could be an old and collapsing fuel line, it could be any, all, or none of the above but a check with an aux tank should confirm or rule that out. You did check the fuel for water and that it's still good - right?
Do you have a fresh, clean, filter/separator installed?

Sometimes it's just a case of walking down the fuel system from start to finish and verifying each component is doing what it's supposed to.

The fact that you had good fuel pressure on the muffs is a good thing. Let's just make sure that it's maintaining and that what it's pumping is the good stuff.

 

[chiswick pride]

Re: VOLVO PENTA AQ170b TUNING PROBLEMS ??

Sorry should have said as it is a project it has new fuel lines & new glass filter bowl which is clean of debris. Tank is secondhand stainless steel but was cleaned before placing in boat.I did think about the vent pipe which was a bit flimsey when I put it in,but soon replaced it with 13mm ID petrol pipe & still did the same(Next time out on the water I might run it with the tube off to see if it makes a difference?
I cleaned the small fuel intake screens which looked clean beforehand,how can I clean the internals further?
How if its lack of fuel am I getting black wetish plugs after only 1/2 hour testing?
we will get there in the end!!