Topic: 750K7 not running right. **Solved**

[ozpacman]

G'day all,

Well I finally got my ex Rhode Island USA K7 registered for the road in Australia last Friday.  Took her for a 200 km (125 mile) run last Sunday however I discovered a few issues.  The clutch was slipping a little, however that was rectified with some clutch adjustment and works perfectly now.

The main issue I have is a lack of power over 4000 rpm.  She pulls beautifully from idle to 4k but then begins to run fluffy.  I fitted new plugs on Monday afternoon to rule that out, however the issue remains.

I noticed that the #1, #2 and #3 cylinder spark plugs looked quite clean and normal however #4 was decidedly sooted up.  No oil residue or anything - just what looked to me to be an overly rich condition with typical unburnt fuel soot.

I drained the contents of each carb bowl into a clean container and there was no evidence of any water or impurities in the fuel.  I measured the quantity of fuel that came from each bowl and the four were identical, so I'm assuming that the float levels are all very close to each other.

I plan to remove the carbs this weekend and have a look inside them.

The way is changes right on 4000rpm makes me wonder of the main jet on #4 carb may have fallen out or something.

Any tips on what you think it might be?

Cheers,

Russ

[martin99]

I think the gurus are going to want a little more information.
Stock setup?
Jet sizes?
Exhaust?

Did you do a plug chop at 4K or take them out when you got home? If the latter your plug condition is not really representative of what is happening at 4K.

Assuming none of your jets have fallen out, in my experience lack of power in mid-range normally indicates a lean condition. Your carbs if PD41s will have adjustable needles which I would check to make sure they are in the stock clip position (if running a stock airbox). If running a non-stock setup try raising the needles by one clip position.

Before you delve into the carbs, you might want to check that your inlet rubbers are sealed tight.

[ozpacman]

Thanks oldskoolnuts,

Yes, she's as stock as a rock this one.  Standard air cleaner, pipes etc with no mods whatsoever.  Bike has only done 7600 miles since new.  The guy I bought it from mentioned that the carbs had been 'adjusted' however I don't believe they were stripped and cleaned etc.

I'm looking forward to getting in there and having a look.

Russ

[martin99]

One more thought, might be something as simple as a duff plug. Could try swapping over and see if the problem follows the plug. Best of luck.

[Stev-o]

First off, confirm you have spark on all four cylinders, check the exhaust temp by the head.  A wet towel will keep you from burning your finger, or use a temp gun if you have one.
If good, I'd suggest a full 3000 mile tune up including a good carb clean/rebuild since you don't know when it was done last.

[70CB750]

+1 on 3000 miles tuneup.

How is the air filter?  The reason I ask is, that I had the very same experience - she would not go over 4000 rpms.

After messing with it I found that my out in the elements air filter got soaked with water after prolonged riding in rain and was choking the engine.  Cutting holes in the filter fixed it instantly.

[Vinhead1957]

Don't forget to measure your plug caps. Especially #4

[jprochnow]

I have a simular problem. I'll look into some of the recommendations.

[seanbarney41]

make sure ignition advancer is lubed and operates properly

[ozpacman]

Well I had a play with the K7 today. 

Pulled the airbox off and checked the air cleaner and it was all nice and clean.  I think it's probably the original element that she left the factory with.

Dropped the carbs off and took them down to the shed for a look.  I removed the float bowls and everything was very nice and clean.  Removed the main jets and tubes and they were all like new.  I measured the float levels and the one on number 4 carb was marginally low so I adjusted it to spec. 

Reassembled everything and refitted the carbs, paying particular attention to the carb to head manifolds and clamps as well as the carb to airbox rubbers and clamps.   

I wasn't really convinced that I'd found the problem but went for a little test ride anyway.  I'm very happy to report that flutter has gone completely and she pulled like a schoolboy!  I ran it up to 6000 through the gears and the old dear pretty much hitched up her skirts and bolted for home. 

I'm a very happy little vegemite!

Cheers,

Russ

[70CB750]

The worst scenario - it works, but you don't know why

[ozpacman]

The worst scenario - it works, but you don't know why

You're right there 70CB750! 

I'm leaning towards the float level as being the main culprit.  As the revs rose and the fuel demand increased there was just not quite enough juice in the float bowl. 

It ran fine up to 4k but then faltered above that.  Running the engine in neutral it was fine but under load the problem surfaced.  So the more I think about it, a supply issue starts to make sense.

Anyway I'm not going to try and over analyse it.  It's just before 6am on Sunday morning here so I think I might head out and enjoy the fruits of my labour!

Cheers,

Russ     

[martin99]

Nice one! Thanks for getting back and letting us know how you did, even if you're not sure how you did it