Engine baulking at full throttle

[Greybeard]

I've just been for a spin. While gunning, (65mph +) the bike on a fast bit of road something occurred that's never happened before. The engine seemed to suddenly baulk at full throttle. If I eased off a tad the engine was ok. I quickly pushed open the reserve tap and the problem cleared. I then shut the reserve tap and tried to repeat the problem. All seemed OK, but I was now on a quieter road so I'm not sure if the problem has gone away. I was wondering about muck in the jets that got flushed through. Thoughts?

[RDfella]

Sounds like a plug chop to check that the main jet size is correct would be in order. Of course, there are any number of gremlins lurking which could cause this. Wrong plug heat range, air vent in fuel tank not clear, constriction in fuel lines anywhere (including tap and float needle valve). Or Brexit.
I'd pull the fuel line off the carb and check for flow. If that's OK, I'd go for a plug chop.

[Greybeard]

Sounds like a plug chop to check that the main jet size is correct would be in order. Of course, there are any number of gremlins lurking which could cause this. Wrong plug heat range, air vent in fuel tank not clear, constriction in fuel lines anywhere (including tap and float needle valve). Or Brexit.
I'd pull the fuel line off the carb and check for flow. If that's OK, I'd go for a plug chop.

I'll do all that. Thanks. I'm happy to blame Brexit!

[Greybeard]

Ah, just had me a little thinkee. Yesterday I removed the thick fibre heat insulator behind the carb because I suspected it of leaking and I didn't have a new one. Do you think the carb may have overheated, causing fuel vaporisation and hence starvation? Seems that opening the second fuel tap may well have overcome the problem.

[Triton Thrasher]

Don’t guess. Start by checking flow right through to a jar under the jet holder.  How many ml in a minute?

Heat transfer does not usually show symptoms at high speed.

[Greybeard]

Thanks TT.

Don’t guess. Start by checking flow right through to a jar under the jet holder.  How many ml in a minute?

How many mls is good or bad? Or am I just looking for a decent flow?

Heat transfer dows not usually show symptoms at high speed.

Ah, ok, back to the drawing board!

[morris]

Had a similar problem on the plunger. Turned out to be the (homemade) air filter restricting the air flow at full throttle. Removing the filter cured the problem

[Greybeard]

Had a similar problem on the plunger. Turned out to be the (homemade) air filter restricting the air flow at full throttle. Removing the filter cured the problem

Well nothing new has been done to the air filter that's been OK so far. I did clean it a while ago.

[Worty]

I'd certainly check the fuel if opening reserve cures it.  TBH, I'd run with reserve open and see how you go for a bit.  If the problem doesn't repeat, then it would seem a fairly simple process of checking for fuel issues.  On occasions, when the ol' girl is struggling up hills with a headwind, I open reserve to see if that'd help ..... and it does a little.  Last time the taps came off there was some light fouling of the gauzes but nothing much.  I do remember on my old Yams that they went like stink when about to run out of petrol - does a similar principle apply here??

[kiwipom]

Don’t guess. Start by checking flow right through to a jar under the jet holder.  How many ml in a minute?

Heat transfer dows not usually show symptoms at high speed.

Love your posts T.T. Straight to the point, cheers

[Ted_Flash]

Hi GB,

I recall reading that you set all your tappets to 8 thou following your rebuild.  They should be 10 and 16.  When the engine gets hot and things expand valves get propped open with insufficient valve clearances. (though it does make the motor sound sweet as a nut when ticking over).

[Greybeard]

8 thou is recommended for the Road Rocket and Super Rocket. I don't usually ride hard so I hope 8 thou is not too close. Can I see other opinions please.

[muskrat]

G'day GB.
Closing the throttle a little richened the mixture. So if it's not a flow problem it needs a bigger main.
Yours is an iron head, RR & SR are alloy. I know you have a 356 cam but I'd still be looking at 12 & 14. It could have been as Ted said. When this happens it only takes a bit of a back off or more fuel to get them back working.
Cheers

[BigJim]

Just for fun. Have you fitted a new seat? Could affect airflow to carb
Feeling cheeky.
 

[Greybeard]

Just for fun. Have you fitted a new seat? Could affect airflow to carb
Feeling cheeky.
 

Stop feeling my cheeky will you!