Triumphrat

kiwee

Can anyone help me with my '81 TR7?

Since Ive had the bike I have had an ongoing problem with it running real rough in the last 1/3 - 1/4 throttle. I would describe it as almost bogging down like it is starving from fuel and to get up any sort of hill you have to shift down to 4th.
Going through the gears up to this point it runs exceptionally smooth, plenty of power, no missing/starving.

So far I have replaced/done the following, and while it has smoothed everything out I cant get rid of this problem.

Carburettor - complete - Brand-new
Plugs
Plug leads
Air filters
Valve clearance, set, checked & triple checked.
Ignition is standard electronic - checked with strobe as per manual. (I don't know what else can be done here).

The only thing I haven't touched is the coils? However they tested OK with a test meter as per the book. But I have heard they can break down under load? Is there a test for this?

Any help appreciated before I go mad.

peintremondain

it looks very much like you have a too small main jet as the main jet is working on the last 1/4 of throttle opening.
later triumph were under jetted to accomodate to laws on the air pollution in the usa.(like hd too)
try a larger main jet
ben

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theelderrocker

Hi Kiwee-
Stock pipes/silencers?

Mike
Kansas, America

kiwee

yeah, stock pipes (unbalanced) and silencers. Main jet is 270.

CommandoRdster

I concur with peintremondain,even if he would like you to throw away your beautiful, wondrous Amals, and install some carbonator with an unpronounceable name,made on Mars or something.
:jest:
The symptoms you describe are classic examples of under size main jets.

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peintremondain

yes commando ,amal are wonderfull because evrytimes i look at them i wonder ......
ben(from mars) :razz: :razz: :razz: :razz: :razz:

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kiwee

Thanks for the answers.

Can anyone suggest a good main jet size as a starting point?

also...

Jet Sizes... what does the number relate to, eg 270?

CommandoRdster

Sorry, I didn't read your original post carefully enough. I see you already had the problem, and you replaced the carburettor in an attempt to fix this problem.That doesn't necessarily mean that the carb is set up properly, but since the symptoms did not improve or change, I think we need to look elsewhere. It seems like a 270 main is plenty large enough, if not too large. I think that I am running a 260 in the single Mikuni on my Commando. The larger the number, the "richer"the jet.
I was going to suggest that you check the float level. Low fuel level in the float bowl will cause lean running at high rpm.When you depress the tickler, does fuel come out within a couple of seconds, or does it take several seconds. If the latter,your float is set too low.
You have checked fuel flow to the carb from the tank? Filters,petcocks, lines,and vent all clear?
Does it do it any time you are at full throttle, even at lower rpm, or just at high rpm? In any gear, or just high gear?
What color are the plugs? Are you getting a fat blue spark at the plugs?

Don't worry, we'll figure it out!

:chug:

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CommandoRdster

Hey, Ben say what you want about the glorious Amal! :lalala:

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okiecityflash

I'm running a 230 with a 3 1/2 slide cutaway on my '79 with free flowing filters and straight thru mufflers. 270 seems big enough to me. Did the '81 have Bings? I think the '80 did.