ESE's works engine tuner

[F5 Dave]

Brass is a swine to drill you are supposed to modify bits to do it properly.

I've done it before with normal bits with 50% success, but not that big.

I drop a ball bearing in hole and give it a smart tap to make seat best it can.

I've also cross drilled the carb body. Drill out the ball bearing and see how small the cross drilling is. 24mm mikuni flat needed this, maybe meth needs on bigger ones?

[Flettner]

you re a little short of travel on that was it dt360? frame.
the dude on the cr125 at 355 or so must have massive nuts.

I think so, I dont remember when it changed. Its been DT frame for a long time now, way better than the shit old Kawasaki one.

[pete376403]

One of the speedway bikes i raced against had a Wal Phillips fuel injector, very similar to the Lake. Philiips was an old racer from way back in UK
https://www.britbike.com/forums/ubbt...IPS&Search=tru

[Frits Overmars]

Restricting the flow to the float bowl used to be a trick in the 100cc direct-drive kart era to automatically lean the mixture when running WOT on the straight, to wring some extra revs out of the engine. Quite risky....

Yes Frits the drivers back then were well versed in running very lean at WOT then semi choking the carb for the last 1/3 of the straights.

Those were the days when you could pick out a top 100 driver in the bar by the short fingers...

The innocent young readers among us may feel the need for some further explanation regarding those short fingers.
Putting a hand over the carb bellmouth can be a risky business on a rotary inlet disk engine with an open chain drive directly from the crankshaft to the rear axle.
I've seen riders taking their right glove off after the race with a finger tip still in it.

Wob, running lean at WOT and semi choking the carb for the last 1/3 of the straights was indeed semi-common practice but it never made much sense to me.
What you needed with those direct drive engines, was a clean pull out of the corners, so you would fit the shortest gearing that would not cause too much loss of time on the last part of the straight where the engine would run out of revs. Running lean all the time and putting a hand over the carb at the last part of the straight would seem counterproductive.

On the other hand (pun intended) putting that hand over the carb when you went off the throttle could be an engine saver. But I was rather careful with my riders' fingers so I gave them an ignition cut-off switch coupled to the brake pedal. That way they could keep both hands on the steering wheel at all times, driving WOT even while braking, providing the engine with lubrication and internal cooling.

Now for the trick with the restricted flow to the float bowl. Driving WOT would cause a gradual drop in float bowl fuel level and an accompanying leaning of the mixture.
In the twisty parts of the track WOT would never take more than two seconds, but on the straight it would start making a difference.
Like I said, it was a risky bussiness, and putting a hand over the carb would not do much good if the fuel level in the bowl was too low.

the other mod that might help
https://thunderproducts.com/product/...bowl-extender/

What good would an extra volume of fuel do if it is too low in the bowl?

[Grumph]

What good would an extra volume of fuel do if it is too low in the bowl?

I've had to deal with fuel surge in the course of working with sidecars. If there's a central nut on the float bowl, an extension to deepen the area the mainjet picks up from - and an extended mainjet to match - works just fine.

I'd assume an extended mainjet would work satisfactorily with that deepened float bowl. It would at least extend the time before running out of supply.

I also agree with Dave above. Look at the fuel passages from hose to top of float needle. If necessary, drill out the unused side and feed from two taps to both sides of the carb.

[wobbly]

Just as it was back in the 100cc days the top peddlers now use the hand choke idea in KZ.
The jetting can be set on the dangerous side of safety and this boost of leaness can be optionally used to make a pass or catch a competitor.
When its not needed during the race a hand in front of one of the airbox inlets drops the egt by 30*C, safe as.
Really good guys know exactly how much they can get away with , and realize you dont have to take the piston home after tech.

[pete376403]

Brass is a swine to drill you are supposed to modify bits to do it properly.

grind back the rake on the cutting edges to almost nothing, (as told to me during my apprenticeship)

[TZ350]

We have been using a very handy 4L fuel bottle setup made by Speedpro for use on the Dyno. Worked very well but maybe time to up size the fuel line and fittings for Methanol.



The inlet fitting is 5.5mm ID but the brass ball is 4.5mm so it looks like the cross drilling needs up sizing too.

[F5 Dave]

Drill it out and you may find the cross drill is 3.2mm or something silly. Then plug again checking that doesn't impede flow. I use a bolt cut down to 'not much', and Devcon. View down inlet to check.

On the 24mm flat mikuni the cross drill broke through to the outside world half way along so more Devon and Re-drill. Shouldn't be a problem on bigger carb.

Short tracks hide this often. Big tracks expose restrictions.

Sometimes through gears 1 to 6 with big roller like on dynojet I could see tall gears getting worse.

[Larry Wiechman]

We have been using a very handy 4L fuel bottle setup made by Speedpro for use on the Dyno. Worked very well but maybe time to up size the fuel line and fittings for Methanol.

I don't trust gravity to get the job done. A stack of diaphragm pumps and a pump-around system will keep the mainjet from sucking wind.

[Flettner]

Yes, I used a modified Honda 50 oil pump to pump E85 around a circuit, past the Lake Injector and back to the top of the tank. So as to keep a constant head of pressure no matter what fuel level was in the tank and to be sure there was fuel at the injector at all times.
I used a flat sided needle ( much like Smart Carb use ) but to tune Id solder, file and measure out at the track until I got the thing to run nice all throughout the rev range. Almost needed a little witchcraft to tune.

[TZ350]

Up sized the fuel line and tap plus the float valve. Followed F5 Dave's suggestion for seating the float needle. Worked Ok.

Even with the bigger fuel line there were no apparent improvement to fuel flow, it still ran like a bag of Poooo with the hiccups. I will have to explore F5 Dave's suggestion about drilling out the cross drilling in the carb itself and get one of those float valves Wob suggested.

Otherwise I might have to look at Grumph's and Larry's idea of a fuel pump.

Also I found the cylinder base nuts had worked loose again! It had been reliable before I pulled it down for re balancing. I am surprised to be having this problem again. Are NordLock lock washers single use?

[F5 Dave]

Saw an interesting ooh-toob test on locking fasteners in weekend. Nordlock not covered. Found the old fashioned split washers were pretty good as were nylock (tested vold) and nuts with lock included. Those usual serated flange nuts often used on barrels were sub-optimal.

[Grumph]

Said it earlier when this problem came up - use Cone lock nuts. Do try it.....

Example - A sidecar outfit rear brake disc was continually coming loose with Nylocks on the retaining screws.

Cone locks fixed it.

[husaberg]

Now for the trick with the restricted flow to the float bowl. Driving WOT would cause a gradual drop in float bowl fuel level and an accompanying leaning of the mixture.
In the twisty parts of the track WOT would never take more than two seconds, but on the straight it would start making a difference.
Like I said, it was a risky business, and putting a hand over the carb would not do much good if the fuel level in the bowl was too low.

What good would an extra volume of fuel do if it is too low in the bowl?

One of the ways i used to establish it was too lean was to wind off the throttle a smidge whilst maxed out to see if it gained revs. If it did go richer
it must have momentarily enrichened it or just went to a less lean state. not sure which, but it used to work for me at least. But was never on the ragged edge.