Rev 3 270 - Fueling And Ignition Timing

[pindie]

Thats a nice guide which sums it up nicely!

[theflyingferret]

Thanks Peter...that's much better than me attempting to tune it through trial and error.

It ran fine today, the 116 Main was fine up to 7/8 throttle...at full tilt it started to bog. I'm not sure if this was too rich or too lean. I'll try my 118 and see if it makes it better or worse...

It's developed a small trans fluid leak now.....grrrr

[pindie]

Whers the leak from? Its an easy fix in the gear lever shaft seal is gone.

[theflyingferret]

Quick update on the VHST26 tuning....

I re-packed the silencer this afternoon, ran it for a while and then followed the tuning guide for the Idle (aka Pilot) Jet that Peter provided. Unlike the Mikuni and Keihen the Dellorto has a Fuel Mix screw to adjust rather than a Air Mix screw...so the Lean and Rich guides have to be reversed.

Anyway, it seems like for the ambient temps and the elevation I'm running at that S38 Idle Jet is too rich. 0-3 turns out does have a small effect on Idle RPM, response etc but even with the Fuel Screw fully bottomed out the bike still idled without issue, it ought to have struggled and required more throttle application. This may also explain the start up issues I'm having and why it's easier to start without the Choke. I've ridden a few other bikes lately, admittedly newer models like an '09 Sherco (Dellorto PHBH26) and a '12 Evo (Keihen) and the throttle response compared to my Rev 3 is drastically better. I know the engine's older, and an older design which probably has more flywheel but I just don't believe the difference should be so significant. I'm going to order the next size down Idle Jet and see how that runs.

The Main 116 Jet is still in it. It's either still lean or now rich. As I very rarely use full throttle I haven't worried about it too much yet. I do have both a 114 and 118 to try but my time is better spent getting the Idle Jet right and Fuel Mix screw set right first.

[pindie]

Have you checked to see if you have a flywheel weight fitted on the Rev 3? My 200 did and was much better to ride once it was off.

[theflyingferret]

I've seen a few threads about the Flywheel weight Pindie but I thought this was only on smaller engine Rev3s in the UK only? Do you have a picture of what the weight looks like? I've had my flywheel off twice and don't recall it being anything other than one solid steel piece. There are threaded holes in it but I don't think anything is bolted up to it.

Is the Weight on the inside or outside of the Flywheel?

Wonder if people have lightened them on a lathe to get the engine to spin up more quickly? (we used to do this with Go Kart engines).

As for the gearbox fluid leak. It needs a new casing gasket, the gear lever seal is fine...ironically the fluid is coming out of the top of the casing/engine joint, not the bottom. It's a slow leak, I'll just keep topping it up until the gasket arrives and I can find time to change it.

Cheers...

[pindie]

Its a flat metal disc about 10-15mm thick with a chamfered edge. If you can see your stator etc you don't have one fitted. If it looks cover with a metal case you may have one fitted.

I try to post a picture....

[copemech]

Eh, the fact that the fuel trim screw is not shutting off fuel at idle, combined with the fact it starts(enrichened) best without choke are an issue.

The trim screw should cut fuel off when full in, reguardless of jet size. This seems to tell that it is drawing fuel from another source. The only other logical source seems to be through the choke circuit, and it seems there is a rubber seal at the bottom of the choke plunger that is designed to seal off the passage to the choke jet when closed. I suppose if that rubber is knackered fuel could be drawn up still providing a constant enrichment.

As we have no history on this carb as to where it came from anything is possible. I thing a poor o-ring seal on the choke jet where it sets into the bowl may add to this problem as well.

Just thoughts, I think Splatshop keeps there parts.

[copemech]

As a second thought on this, if you have it idled up too fast whan setting the mix screw it may be possible to draw fuel from the transition circuit orface(just behind the slide) so do your screw setting at low revs just poping along.

[pindie]

If it helps I set my tick over only up a tad. I test by standing by the bike and put it in third gear. If I can let the clutch fully out whilst not on the bike and then walk beside it I know its right. Not too high its ring ding dingging but just enough so you can use less throttle action at fine moments. Probably no good for better riders though?

[theflyingferret]

Copemech! You've had me wondering about this for days now!

I could well be wrong but I don't think the Fuel Mix screw can shut off the fuel supply through the Idle Jet completely can it? I just don't see why Dellorto would design it this way, I can't think of an application that wouldn't require some level of ability to idle.

Have a look at the section view here:

http://www.ducatimeccanica.com/dellorto_guide/fig18.jpg&imgrefurl=http://www.ducatimeccanica.com/dellorto_guide/dellorto_3_4.html&h=332&w=250&sz=19&tbnid=9BvYRKixeXz8kM:&tbnh=90&tbnw=68&zoom=1&usg=__TuSpbwSg40u8paK_ejI1YD6CbZc=&docid=TtWWmwxpq9l-_M&sa=X&ei=NZYpULfaB-nh0QHT24HQDA&ved=0CFwQ9QEwBQ&dur=1

The screw tip doesn't have a proper seat to seal against...and in any case you're right, the Progression Port should allow some fuel to get up to the Venturi through increased vacuum if the flow through the Idle Port is minimised.

An S36 Idle Jet is on it's way to me from the UK (apparently via a rather poorley carrier pigeon)...no VHST bits in the US.

I've learned more about Dellorto Carbs in the past few weeks than I ever wanted too!

As for actually setting where the Fuel Mix screw should be I'm still confused...there are a lot of conflicting methods and different opinion on what you're supposed to be looking for out there.

[copemech]

Copemech! You've had me wondering about this for days now!

I could well be wrong but I don't think the Fuel Mix screw can shut off the fuel supply through the Idle Jet completely can it? I just don't see why Dellorto would design it this way, I can't think of an application that wouldn't require some level of ability to idle.

Have a look at the section view here:

http://www.ducatimec...FwQ9QEwBQ&dur=1

The screw tip doesn't have a proper seat to seal against...and in any case you're right, the Progression Port should allow some fuel to get up to the Venturi through increased vacuum if the flow through the Idle Port is minimised.

An S36 Idle Jet is on it's way to me from the UK (apparently via a rather poorley carrier pigeon)...no VHST bits in the US.

I've learned more about Dellorto Carbs in the past few weeks than I ever wanted too!

As for actually setting where the Fuel Mix screw should be I'm still confused...there are a lot of conflicting methods and different opinion on what you're supposed to be looking for out there.

Although I do not currently have the PHBL installed on my bike, as I recall the fuel trim screw would indeed cut all fuel at idle when the flat hit the end of the passage(does not jamb the taper end in the hole). Bike will die out if this is not done really quickly to get a turn count when running.

Now the PHBL is not exactly the same as the VHST, yet with exception of slide design they are very similar it seems and many parts the same.

As the pilot circuit is behind the slide, it is exposed to vacume, which literally sucks fuel in, now the transition circuit being in front of the back edge of the slide would rely more on venturi effect to pull fuel, and without the slide cracked more this is unlikely to happen, at least in my theory of current understanding.

Did you not say you had another bike around with a dellorto? Try a PHBL and see what happens.

[theflyingferret]

I do have a rather dirty and dusty PHBL26 laying around. It's worth a shot, I'll find time early next week to clean it up and fit it....by which time the new Jets for the VHST will probably have arrived.

I rode the bike mid-week...the first half an hour the Fuel Mix screw was completely bottomed out in the Carb and I had no idling problems...just ****ty response. I almost hope that you're right CopeMech and that there is indeed some kind of fuel leak path that needs idnetifying and correcting. It would explain a lot of things including the terrible starting issues, the response problems...perhaps even the flat running of the engine at top-end.

Last time I had the Bowl off I checked the O-Ring on the Choke Jet and it looked fine...I suppose it could be anything though, a crack in the carb somewhere, over drilling of a passageway....who knows.

We'll see what happens with the PHBL.

[theflyingferret]

Alright. Finally made some progress with this infernal contraption! Last 2 weeks I've had no time to do anything, but finally I got my new Jets and found some time today.

VHST out, stripped, thoroughly cleaned with compressed air and carb cleaner...The main 116 is now a 114 and the idle 38 is now a 36. I also took out the reeds, they're perfect.

So, I have done no running except for a quick squirt around the garden. The point is that without trying to set up either the idle or fuel trim screw the thing started 2nd kick with the choke on. I know, madness eh? Yes, to most a very underwhelming development but to me, this is massive! It was a pleasant surprise from the usual kick it over 25 times for it not to start....take out the plug, pour fuel down the thing, refit the plug and then kick it over before it goes. The only thing I found amiss with the carb was the choke plunger o-ring...it was either out of place the whole time or I disturbed before noticing when I took it apart...anyway, I seated the o-ring properly, maybe this made the difference...

I wanted to take it for a proper ride and fine tune the carb in with the new idle jet but have been hampered by brake issues. The front brake has dragged since I've owned it. The brake itself works really well and is nice and progressive but it drags to the point where the bike is a pig to push and just to add further annoyance the damn thing squeals like the piggy that went all the way home.

I split the caliper, got the 4 pistons out courtesy of my air compressor (this works great by the way, but if you're going to try it be prepared to watch them get some serious altitude as they "pop" out of the cylinder! Wear some goggles please...). I cleaned everything out, nothing seems corroded or marked, the seals looked fine. Put it all back together, got the caliper as central to the disc (which is straight) as possible and filled them backwards with fresh dot 4 using a syringe. Bled the system as effectively as they can be.

The result: Again a great front brake....again a squeal and mass-dragging. So, for whatever reason at least one of the pistons isn't backing off. Has anyone out there had this issue, more importantly does anyone know the the root cause and how to fix it? Hydraulics are simple systems so it can only be one of a few things. Are the master cylinders prone to breaking down internally? Do the Rev 3s have known caliper issues?

Answers on a postcard....!

[copemech]

Well, I would suppose you know to insure the pin on the master cyl is returning fully so no pressure is being held into the line. Other than that, the O-rings on the pucks are what actually flex and release tension on the pads, which must float freely. You did not put new O-rings on the pistons? If they are old they may have lost their flexability. Just a thought.