Triumphrat

hayabusaman0

Hi All, can anyone tell me why the choke jet hole in the brass tube fitted to the carb is slightly smaller than the jet in the float assembly? The reason I ask is because I am fitting these to my pushrod trident & it is a real bastard to start,so I am thinking about drilling the jets out.

Thanks in return, Paul.

GeoffE

Hi Paul,

Please can you relate the part to the number on the diagram given for your previous post?

Which particular model did the carbs come off of, or what size main (/pilot) jets are fitted? Have you enlarged the inlet stubs &/or changed the connector size, etc.... Have you fitted pods, or modified the airbox?

Also, can you update your profile to show your location.

Fyi, I am currently doing a similar thing (Mikuni BST carbs from a Hinkley 750 Trident) but to a Yamaha XS850 triple. Also I have a '72 Rocket Three triple (sister bike to yours). If you like, send me a PM with your email address, and I will try and help.

Geoff

hayabusaman0

Hi GeoffE, Royston, Herts is my location, carbs are from 900 Daytona(K582) fitted with std T150 air filter, inlet stubs are from Triple Cycles & are used to fit the 30mm carbs to a std head & commando inlet rubbers, I will have to check jet sizes. Are you in the TR3OC or do you go onto Triples online? I have not seen the diagram yet.

Regards, Paul.

GeoffE

Hi Paul,

Apologies but I did not understand the 'K582'? Anyhow here is the schematic linked in from Bike Bandit:

I think you may find the two outer main jets (14) to be 125, and 120 for the middle carb, assuming it is standard. People don't normally change anything else (unless a Dynojet kit has been fitted), with the pilots (11) being 40s, Needles (7) being SE56-3s and Emulsion tubes/Needle jets (13) being O-8. The Clip (5) is normally set on the 3rd groove of the needle (7) and can be raised or lowered to fine tune the rich/lean mixture. Float height should be 14.5mm.

The Mikuni main jets are coded N100604-xxx (where xxx is the main jet size), also know as the 8mm large round slot head type, and cost around £3 each from Allens Performance (tel: 01949 836733). Ideally you should have all 3 main jets the same, as your airbox does not have the restricted centre of the original Daytona airbox.

Yes, I am a member of triples online, but I cannot remember seeing a suggested main jetting for the Meriden triples, so I think you may be on your own? Fyi, if it helps, I do know that there are two XS750 triple owners who are using the same carbs as you successfully, with only the clip moved 1 slot to lean out slightly.


Just a final thought - there is an old motorcycle adage along the lines: Problems starting from cold, suspect the electrics. Problems starting when warm, suspect the fuelling.

Hope this helps?
Geoff

hayabusaman0

The 2 jets I am on about are- 1 is fitted to float assem #19, this had 0.7mm hole & in the bottom of the carb there is a brass tube which fits inside the float assem & connects to the link tube (on outside of carb) which feeds fuel to the choke operating lever #10(this has 0.5mm hole). K582 is the model no stamped on the carb body next to the serial no. The starting prob is def fuel related because if I inject fuel thro' the vac take off points it fires straight away. In the Trident & Rocket Three Owners Club there is at least 1 guy I know who has fitted these carbs, he has the same trouble starting, mpg is about 50, it a lot better slow running & smoother but mid throttle performance is not as good as the Anals(not a spelling mistake!). When I had mine fitted I was impressed at how smooth it was. I guess the lack of performance is due to the carb being 36mm & not enough air speed to drag the fuel up.

Paul.

GeoffE

Hi Paul,

I'll take a closer look tomorrow, but a quick question for you.

The T150 manifold/spiggots don't have a vacuum take off, and I suspect the Triple Cycles 30mm inlet stubs perhaps don't either? What have you done with the vacuum ports/pipes?

Geoff

hayabusaman0

The vac ports are situated on top of the carbs, already blanked off with sealing rubbers.

GeoffE

Hi Paul,

I don’t know if this is going to help, or if it is just ‘telling you how to suck eggs’? Apologies if it is.

I guess the jet fitted to the float assembly is the needle jet, controlling the fuel fed into the bowl? It should not matter if this is smaller than the choke jet as the bowl is acting as a ‘header tank’ to the choke jet?

Another thought about the size of the choke jet is that the choke on a CV carb is only an enrichment circuit (i.e. adds to, not replaces). I found this reference: “The choke system is used to start cold engines. Since the fuel in a cold engine is sticking to the cylinder walls due to condensation, the mixture is too lean for the engine to start. The choke system will add fuel to the engine to compensate for the fuel that is stuck to the cylinder walls. Once the engine is warmed up, condensation is not a problem, and the choke is not needed”.

The cold starting procedure for a CV carb is different to the Amal (where you position the throttle to ¼ turn approx), indeed the throttle should not be touched at all with a CV carb. This is confirmed by looking at a number of User Operating Manuals for machines fitted with CV carbs. I found this reference: “Remember not to pump the throttle, as the choke on the Triumph Mikunis uses a separate enriched fuel circuit and hence does not benefit from throttle activity. On the contrary, opening the throttle will just lean the mixture right off at this stage. The throttle should not be used at all until the choke circuit has done its work and the engine is firing”.

So I am guessing you may be using the throttle at start-up? This is ‘leaning’ out the effect of the choke, and together with the use of only a kick start lever (I assume – T150?), is not as efficient as using a continuous electric start with the full choke enrichment. (By injecting fuel through the vacuum take-off, this may have offset any ‘leaning’ out caused by the use of the throttle, hence you firing up the bike immediately)?

Do you think the starting problem could be through the use of the throttle?


Another couple of comments/thoughts:

“Mid throttle performance is not as good” – you may be able to improve throttle response slightly, depending on the current vacuum porting you have in your pistons. Dynajet use this technique in their kit – see http://www.dynojet.com/pdf/5102.pdf. I think the drill bit is 3mm?

36mm carb down to 26mm inlet port size (via 30mm stubs)? – I guess you have tried to smooth out this path out as much as you can? I just wonder if this ‘restriction’ may have more to do with your lack of “mid throttle performance” than anything else?

Hope this helps?
Geoff

hayabusaman0

Hi GeoffE, if you have the float assem in your hand you can see that the jet in the plastic part only feeds the choke circuit, & you are quite right in saying that not to use any throttle when starting, the inlet stubs had been turned up on a lathe so there aren't any steps as such, I tried it with the extra lift hole in the slide which didn't make any differance which is why I think the air speed is too slow until it gets to 5k & then she goes well, I might try without the slide springs.

Many thanks,Paul.