1972 Bonneville T120rv Perfomance Issue

[oldbloke]

My old bike will Rev to well over 6,000 rpm in neutral, on the road she gets up to 60 mph approx 4,000 rpm and refuses to go any quicker. I have checked ignition and valve timing which appear to be OK. When at 60 mph shutting the throttle very slightly the bike feels as if it wants to go faster. Is this a fuel issue ?. The carbs were rebuilt before I got the bike, and all the internals are as per workshop manual recommendations. This has been ongoing since I got the bike and it's driving me mad, any of you guys come across this before ? Any suggestions/ideas will be gratefully received.

 

[grandpaul]

Do your carbs have the enricher "choke" slides still installed?

If so, you need to ensure that when you pull the choke lever to tighten the cables fully (extracting the slides from the carb throat), that the cables are adjusted so that the slides pull ALL THE WAY OUT of the carb throats.

 

[oldbloke]

The carbs have no choke slides at all. I have also checked the float levels which are correct.

 

[grandpaul]

Could be the cam idler pinion fell out at some point in time, and was re-installed one or more teeth off.

Pull the timing cover and spark plugs, and turn the engine over till the marks align, or 94 turns of the crank, whichever comes first. If they don't line up, it's because the intermediate pinion was installed incorrectly.

If you notice that the marks are CLOSE at any point, simply pull the intermediate wheel and align it then and there. Nip it all up, carefully re-set the ignition to it's proper static timing, fire it up and strobe time it, then see what you've got.

 

[oldbloke]

Checked valve timing - OK, Checked ignition timing - OK. No difference in performance.
Do you think it is possible that the gearing may have been messed with, or could the carbs really be that far out ?.

 

[harper6t]

Blocked air filter ?

 

[grandpaul]

Definitely check the air filters, but it sounds like the previous owner or whoever worked on it, mis-timed the cam drive gears. They will NOT "re-time" themselves.

 

[oldbloke]

Both air filters are brand new and perfectly clean, Have checked valve timing and it is right

 

[grandpaul]

HOW did you check the valve timing?

Typically, that must be done with a dial indicator and a degree wheel...

If you mean you visually verified that the cam wheel timing marks are all properly aligned, then we need to study other possibilities.

 

[oldbloke]

Set T D C with Triumph tool located behind cylinders. Removed idler gear and reset all the timing marks. Had to remove the oil pump as the Morgo pump covered the marks on the inlet cam.

 

[grandpaul]

You're sure you set TDC, and not 38d BTDC? I don't recall, but that flywheel might have both notches.

 

[oldbloke]

definitely TDC, you are right, the crank does have two notches of which I have both clearly marked.

 

[grandpaul]

Hmmmmm...

Are you sure you don't have the carb slides turned 180 degrees with the cutaway toward the engine?

 

[oldbloke]

Just had the carb tops off and they are the right way around. The bike is fitted with Amal Mk 1 Conc. which have a key at the top of the slide to it can only go one way.
What I can't get my head around is, in neutral the bike will rev at 6,000 rpm plus with no effort at all, yet on the road it is running flat out at 60/65 mph @ 4,000 rpm.

 

[harper6t]

Well, if it was a Velocette my advice would be to take off the air filters and try it like that, because the symptoms you describe fit exactly what happens when you fit an air filter on an old Velocette.

 

[triumph david]

I'm late to this post, have you checked the cam lift, that is the only thing i can come up with. The thing wanting to try to go faster when backing off the throttle at 60 might be a clue but i don't know what. Make's me want to think that a cam was mis-marked.

 

[grandpaul]

The reason I was wondering about the carb slide and chokes is the same as harper6t says, sounds like it's choking.

Could well be a flattened cam...
(I hope not)

 

[oldbloke]

Hope it's not a cam, but it's another thing that needs to be looked at, it may be a while before I get round to it. Any other ideas will be welcome

 

[Jac0b561]

I'm late as well to this, not even sure if this has been resolved yet. Have the carburetors been cleaned in a dunk tank lately? Mine were choking a bit and my bike was lacking in power. A friend of mine suggested the dunk tank, and cleaned out all of the tiny little crevices and holes, and it felt like a new bike afterwards. Turned out a lot of those holes and crevices I mentioned were clogged and it wouldn't rev real high.

 

[triumph david]

Here's something i just thought of it happened on a RD350, and a lawnmower i had. The air flow hole in the gas tank cap stopped up and i liked to have never figured it out. The thing about it is that there can be all kind of symptoms, this one is enough to make a preacher cuss! Might be worth a try to run down the road with the cap loose. Good luck!