Exhaust help required

[Ditchfinder]

So I swapped the end cans on my 94 Sprint to some oval laser cans cos well they looked nicer and stuff (never mind that the bike's a total shit heap, it's a project don't ya know! ) Anyway it was running fine before but now is misfiring and has lost a lot of power.

I thought end can swaps shouldn't make a huge difference to fuelling but was I wrong to assume this?

[Le_Fromage_Grande]

It's probably running lean due to less restrictive cans, go up two sizes on the main jets and work from there, you'll enjoy getting the carbs off and putting them back on again, especially the number of times you're going to be doing it.

I don't know of anyone that tunes Triumphs, but you could try Larry at PDQ Developments, he seems to have experience of most bikes.

[Ditchfinder]

Is it worth pulling the plugs to check before taking carbs off - they are a bit of a sod on these Hinkley Triumphs ?

[Le_Fromage_Grande]

Is it worth pulling the plugs to check before taking carbs off - they are a bit of a sod on these Hinkley Triumphs ?

If you want, but it's going to be running lean if the only thing you've changed is the cans, and looking at the plugs to tell you something you already know seems a bit pointless.

And yes I'm aware the carbs are a bastard to get off and on.

[Ditchfinder]

Ah deep joy **wanders off to youtube to learn about main jets before realising it's probably best to give it to a man to sort out

[Le_Fromage_Grande]

It's pretty easy to change the main jets once you've got the carbs out - getting the carbs out is hard work.
If it's got Japanese carbs buy a set of JIS screwdrivers

[mangocrazy]

The shiny new can you've put on isn't a stubby (or significantly shorter than the original), is it? Stubby cans have a well-deserved reputation for fucking up the fuelling.

[Ditchfinder]

No the cans aren't shorter - been doing some more research following cheese's advice and it does look like the cans I have are a lot less restrictive so will need to rejet the carbs

[ace llani]

remember the plugs will only give you an idea of how the bike was running - when it was shut off.

To get an rough idea of jetting on a race bike. we had to run it on full throttle down a straight at the end of a session (to judge the main jet fuelling) and kill the engine instantly and push back to the pits.

It would benefit from a run on a dyno. you'll never jet a bike off road riding.

Money well spent

[Nidge]

Before you go delving into the carbs is it worth putting the old cans back on just to make sure you haven’t, coincidentally, picked up another problem? Would be a huge pain to pull the carbs and then find out it needed a new spark plug ...

[Ditchfinder]

Going to give the headers a thorough check to see if I cracked anything getting the old cans off or didn't fit the link pipes properly, if I can't see anything obvious the old cans are going back on to check whether the new cans are to blame for the poor running

[bevvo]

Have you done it yet? I'm having a slow day. The suspense is chafing me.

[Ditchfinder]

It's a weekend job bevvo - I'd find yourself some cream to soothe yer chafes

[Ditchfinder]

So old exhausts back on and it's not back to how it was. Below 4k rpm it's running rough, above 4k on part throttle it's s still rough, above 4k on open throttle it runs fine.

What could I have spannered changing the cans over do you think?

[demographic]

So old exhausts back on and it's not back to how it was. Below 4k rpm it's running rough, above 4k on part throttle it's s still rough, above 4k on open throttle it runs fine.

What could I have spannered changing the cans over do you think?

I've not read the wbole thread but could there just be some crap in the fuel and its pulled that through?

[Ditchfinder]

Ok after a tip to check the vaccuum feed to the fuel tap I have discovered there's a non standard line with a fuel filter in it, likely put in to stop crap from the tank blocking the carbs but I'm wondering if this is causing an issue. It wasn't before though so not sure why it would now

[Taipan]

When is it misfiring? Is it spluttering as you crack teh throttle open? Try shimming the needles first

[Ditchfinder]

Nope misfire goes away if I whack throttle open above 4k, anything on half throttle or below 4k and it's no good.

Need to check vacuum pipe off fuel tap next as these get easily pinched due to routing then it's probably off with the online fuel filter then check resistance across coils after that.

[Nidge]

I think I’d start with the simple stuff first; plugs, leads, fresh fuel filter etc. These types of faults can be misleading - what seems fuel related can be ignition and vice versa and once the engine is spinning fast enough (I.e. over 4K) it can overcome a poor spark etc

[Ditchfinder]

Will do, I'm thinking fuel side though as all I've done is swap cans and put fuel in it and it was fine before