Rough running dianostic

[gregvh]

My brat has an intermittent issue that has me lost. I am hoping this will sound familiar to one of you guys.

 

The engine purrs wonderfully most of the time. Proper idle, good power, she is as good as it gets. Then, she will suddenly start running rough. She will die if I let off of the gas. It feels almost like she is missing but the electrical is pretty fresh. The problem happens warm or cold. Once she is running good it never seems to pop up until I shut her off and restart. Even then it is maybe one in ten times she goes wrong. I have noticed that she can start off running bad but occasionally when I get her out on the freeway something will give and the problem goes away.

 

I was thinking maybe a fuel filter?

 

Another issue that may be related. Her oil pressure has been running too high. It floats up against redline. Warm or cold, always the same.

 

Thanks in advance for any help. I will work this out either way but your advice always moves the ball forward.

[Dirk]

Carbed or fuel injected?

[gregvh]

1987 hitachi carb

[ihscout54]

If you havent replaced the fuel filter and inspected your vac system then nows a great time to do it. It sounds like a float/flooding problem, to me. Your going to need to pay attention to whats going on when this happens. Does it puff black smoke when its trying to die?

[Dirk]

Oakie dokie.

 

So if it were me, the first thing I would check is the codition of the vacum hoses. Make sure there are no leaks.

 

Next I would dirrect my attention to the carb jets. I had a very similar condition to yours not so long ago. Turned out to be some crap in the idle jet.

 

For me the problem was only rough idling so that is where I looked. Tell us more about the problem. Does it only idle rough or does the symptom appear at acceleration/light use/full throttle etc? This should give us an idea about where to look. And Yes it could also be a clogged fuel filter.

 

Cheers

 

Dirk

[gregvh]

The problem exists under all driving conditions when the issue is ON. When it is off she is perfect. No smoke noticed but I'll keep an eye on that. No noticeable vacume line suck sound. Btw, my method has always been to listen for the suck sound. Is there a better way to verify that the lines are all good?

 

I noticed an odd thing that might be of use here. I spent some time adjusting the idle last weekend. I set it at about 800. The next day, she was running good but the idle was at about 400. I grabbed a screw driver and cranked her back up to 800. The next day she was running good but idle was now at 1100. I cranked her back down to 800. This morning, running good but shes at 400 again. I feel like this should mean something but it is beyond me.

 

Unless otherwise directed I will swap the fuel filter this weekend and recheck the lines. As to Carb jets, I have never got into a carb too deep. Other than hose it with carb cleaner, any tips there?

 

Thanks again guys.

[GeneralDisorder]

Sticking float - I've seen it multiple times on the Hitachi's. I'm not sure just what causes that, but every time I've rebuilt the carb and replaced the needle and seat and it's never come back.

 

Make sure the tach isn't sticking - sometimes they hang up - smack the dash above the tach when the idle is "high" and see if it comes down.

 

Otherwise the fast idle cam may be sticking.

 

Sounds like a good carb clean/rebuild is in order.

 

GD

Edited November 25, 2009 by GeneralDisorder

[ihscout54]

I noticed an odd thing that might be of use here. I spent some time adjusting the idle last weekend. I set it at about 800. The next day, she was running good but the idle was at about 400. I grabbed a screw driver and cranked her back up to 800. The next day she was running good but idle was now at 1100. I cranked her back down to 800. This morning, running good but shes at 400 again. I feel like this should mean something but it is beyond me.

I played this little game with my BRAT when I first got it. Some one had messed with the idle mixture screw and it was just making my life miserable. There is a reason it is "pinned" especially on the feedback models. Aside from the float, a worn throttle shaft or a sticky secondary will create this condition. Also any unique vac leak will too. Especially a little leak after one of the many doodads (I.E. thermal vac valves)

You know what, I dont miss the Hitatchi at all.

[Dirk]

If something is sticking I wonder if I could be the vacum advance diaphram? If this were to stick a little it would be responsable for rough running and idle issues.

 

Take off the distibutor cap and have a look at the linkage. Could be sticky or maybe worn.

 

Just another thought, Check to see if the throttle linkage is returning fully. Maybe the return spring is a little tired. That would also mess with your idle.