We'll try anything - Carbs (long)

Rebelelf's bike again. 650 frame/750 engine

This bike is running rich as hell and is burning through plugs and gasoline like no other. We've tried everything we can think of but still no luck getting it to run any leaner.

1) Carbs cleaned, 3 times. Last time all jets and pieces soaked for 24 hours and all ports blown out by a high powered air gun.

2) Clunk test is just fine. No holes in the diaphragms.

3) Stock air box and pipes.

4) Main jet is 120, pilot is 40. Main bleed jet is 220, pilot bleed jet is 80.

5) Floats set at 16mm, 17mm(stock), and 18mm. No difference for any setting.

6) Choke is not sticking. Plungers fall and close off when choke is turned off.

7) Air filter is in good condition.

8) No air leaks.

9) Compression is good.

10) Petcock is not leaking and is set to ON or RES, no difference.


We're at wits end with this thing. It's blowing out black smoke and when it back fires it sounds like a shotgun being fired. With it eating through plugs so quickly we're lucky if the damn thing starts anymore.

If you have any ideas we're willing to try anything at this point.

 

On my 650 the main jets are 110.

 

How many miles are on this motor and have you checked the valve clearances?

 

Examine the AIR Jets.
The Book has the sizes quoted in the wrong order.

They should be in there like this:

 

We're not sure how many mile are on the motor. The cluster was changed multiple times by PO and the one currently on it is a Honda SB250 speedometer.

We have not checked the valve clearances because we don't have the tools for it and don't want to pay $450 for the local mechanic to do it.

 

You don't need special tools (other than a feeler gauge) to CHECK the valves. A motor that has a lot of miles with no valve clearance adjustment could very well have all "zero" clearance valves and refuse to run/backfire, etc. I would at least check them.

 

Where can I get a feeler gauge? Or is there a different name for it?

 

http://www.sears.com/shc/s/search_10153 ... utton=find

 

I guess that answers my question. Which one would you recommend or do any of them work just as good?

 

I believe that these are switched, assuming you're referencing the correct air jets. See Rick's photo above.

 

Get the feeler gauge that has .0015" as the smallest thickness.
Mine has .0015, .002, .003, .004, etc.

You want the ability to measure in between thousandths.

 

You can get a feeler gauge at Sears or any auto parts store. That's what they're called. You might want to consider a service manual at this point.

 

I bought mine at my local Sears.

 

Thank you Rick!! The air jets were switched around. Runs fine now. Nice blue color coming from the colortune.

We're trying to get a service manual for it but there's not up on eBay at the moment and a new one is not in the financial plans.

Only problem now is there's an air leak somewhere and we don't know where. We think it's coming from the butterfly shaft on the right side. Is there a way to fix that?

Also, what is the correct orientation for the fuel jets in the bowls and what would be the problems if the fuel jets were switch around?

 

The throttle shaft seals are a unique cross-section, not a simple 0-ring. chacal has the correct ones. You have to split the rack of course.

 

Is there a how-to guide on doing that? I was always told by my local mechanic to never break the rack.

 

i'm sure the only reason he told you not to ever break the rack is because you'll have to re-sync the carbs afterwords.
here is a great how to on changing the seals by schmuckaholic

http://mok.fileave.com/HitachiCarbBreakdown.pdf

i got mine from chacal. i would suggest doing all of them at the same time. good luck

 

Great news! It has risen from the ashes! I'm no guru but from what the gurus on this site say to do is start your carb rebuild by checking valve clearance and adjusting where necessary. You never want to run the valves with no lash because you run the real risk of dropping a valve head through a piston. This always results in catastrophic failure.

You have certainly paid your dues on this bike. Just don't cut corners now. Man, I'm glad to hear you've got it running!