WOT Combat let off surge?

WOT Combat let off surge?

Believe me or not but last week was my first and last time trying to max out on factory Combat Trixie. Oh I'd pressed her WOT a bit now and then over a year but only short enough to sense the dangerous handling till its reactions build up in my spinal reflexes till confident enough to find out what she+me could and could not get away with. Basically just barely good enough to keep up with most riders on sports bikes too scared or lack of skill to press their bikes much to about the ton, but not nearly powerful or safe enough to hang with a rider who does know how to ride sports bikes like they can be in safe thrill zone. Hell a good PU truck can out accelerate and handle a factory Commando.

When I cut WOT abruptly I get an instant of deceleration instantly followed by a whip lash like surge forward then normal engine drag. Its not all drive train lash as chain and gearbox pretty tight w/o clutch wobble or slack. Trixie does not surge forward when cutting WOT short of Hi 6000+ rpm states. This surge is enough to dangerously upset chassis if leaned 45'+ at speed - over 80 in good sweepers.

After 90 Trixie really perks up till at least 110 where I get scared for her stock engine survival. I have not held on to top out Trixie, never will but feels like would pull over 120 before valve float - if I dared. I'm used to 120 mph on Peel and SuVee and don't consider it that fast as aero dynamics don't bother much till then. !20 is my threshold of tucking down.
I don't have to on Trixie to pull strongly as fast as I dare too - so mostly bolt upright only tucking down to lower CoG for entering flings short of full Hinged Horror.

Trixie wears past Peel's 'poorly performing' dual 32 Amals [compared to prior amazing stock single 34 Miki]. I know I know but me and Peel don't know any better how singles suck so bad pulling to top end, nor does Peter with his 40 mm. Amals are slightly modified by race taper needles in middle groove, slot cut in float bowl fuel feed and a 1/16" notch cut in top of spray tubes. Nice response down low to kick out tire right now on loose stuff - BLATT- w/o hesitation that grips too much to throw forward instead of just changing aim. Air enters via factory paper filter air box. Over all seems a tad rich looking at plugs and muffler dark soot, but not that much as requires tickle to start cold but not afterwards unless dead cold again.

What should I think about checking or changing. Spark timing is ~29', just short of kick backs to start and no detonation 87 to 91 octane. I don't press real hard on 87, just in case.

Could it be that the needle taper leans it a tad when you chop the slide/needle?

hobot said:

When I cut WOT abruptly I get an instant of deceleration instantly followed by a whip lash like surge forward then normal engine drag.

Click to expand...

That may be a symptom of the main jet/s being too weak. Closing the throttle sharply from WOT can momentarily richen the mixture-so the bike surges before it slows down.

Hm, I don't know how to really tune Amals, so could well be. i've 2 more sets of factory needles and a range of jets 220 to 260. I think 240 in now. I do prefer to be told what to do but usually end up finding out the hard way, trial error for educational wasted efforts. Wes got these race needles at a rally but made his '71 throttle too responsive to cruise steady state and lowered his mileage so much on peanut size HyRyder tank we switched needles after first 60 mile gas up on 1000 mile trip back home. On Peel I hardly noticed any difference nor any surge with them on WOT 7000++ rpm throttle chops. No chassis upsets either. This surprise hard surge is a new one to me. Not noticed on Trixie much till last weeks fling.

Wil first try raising needles to bottom groove and see what happens then try something else. Trixie has #3 anodized slides to try to compensate for fairly fluted worn out bores and seems too work well for everything but all out destructive level of throttle use.

** Trixie does not surge if letting off WOT just a little - as I've read is a test that implies too lean at WOT. Spray tube notch is only supposed to matter at low rpms and didn't notch as much as Amal supplies them - which should richen not lean anywho.

hobot said:

i've 2 more sets of factory needles and a range of jets 220 to 260. I think 240 in now. I do prefer to be told what to do but usually end up finding out the hard way, trial error for educational wasted efforts.

Click to expand...

Ok then, I will tell you to try the 260 main jets if that makes it easier?

hobot said:

Wil first try raising needles to bottom groove and see what happens then try something else.

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But the needles have no effect above 3/4 throttle. Start with the main jets, that's the way the Amal tuning guide says it should be done.

http://www.amalcarb.co.uk/downloads.aspx
Amal Tuning Guide.

1ST MAIN JET with throttle in position 1. If at full throttle the engine runs ‘heavily’ the main jet
is too large. If at full throttle, by slightly closing the throttle or air valve the engine seems to have
better power, the main jet is too small.

Click to expand...

For reference I have 240 main jets in 932/19 & /20 Amals with the Norris RX camshaft in an overwise stock combat. Not having any carburetion issues, but not ready for WOT yet. Have gone to 6,000rpms...no problems.

LAB thanks for the better seasoned Amal logic for me to apply. I over looked the needles at WOT being lifted out of effect. I've seen instructions for racers to tune jets for WOT power w/o any needles confusing the lower throttle issues.

Help me with a bit more logic scope. These Amals did not surge on Peel Combat, just gave guicker tire spin or leap forward punch below 3000 rpm in my driveway play than the 34 Miki, but Amals lowered response, pull and top end after that. I had to twist further and more ahead of time to approach 34 Miki on hwy use. Also noticed two springs more work than one. Peel could breath a lot better than Trixie, so would Peel's higher flow-velocity inhales enjoy bigger jet or smaller - in regards to Combat base line? My logic implies more velocity pulls fuel stronger so less jet area needed. On the other hand I read if a hopped up engine can burn more fuel > that implies a bigger jet helps, Ugh.

Just running up to 6000 in a Combat is still about like any good ole standard 750 - as doesn't really become a Combat Bomb till 500-600 rpm more then should feel like most another piston kicks in till valves, points, or other bad parts suddenly interfere. Considering that ole braggart hobot took over a year creeping up on maxing Trixie out, I don't feel anyone is being too timid feeling for the MAXing out Combat disappointments. . .

L.A.B. said:

hobot said:

When I cut WOT abruptly I get an instant of deceleration instantly followed by a whip lash like surge forward then normal engine drag.

Click to expand...

That may be a symptom of the main jet/s being too weak. Closing the throttle sharply from WOT can momentarily richen the mixture-so the bike surges before it slows down.

Click to expand...

Classic symptoms of undersized mains, assuming the float levels are correct.

Classic symptoms of undersized mains, assuming the float levels are correct.

Click to expand...

oh Ugh, maylar, I withheld a shameful data point you make me vomit up now...

Dealing with Trixie losing float bowl screws so bowl and gaskets in breeze and fuel pouring out, Wes freaked me out by taking off the fuel hose carb banjos !!!! They were a terror to get sealed w/o distorting/striping. So of course Wes looked both shocked at my reaction and then soon again by how much fuel freely poured out on his normal torque up sense. ugh. After getting that sealed they carbs would not stop over flowing, ugh. Wes said must be the float level, though I didn't agree as had dialed them in for 1.5 ish best idle. But they were flooding and tickler not stuck so had no defense to his logic - as usual. Used my finish nail drift by guess/by golly to lower floats pure frustrated feel, to get flood stopped and pilot screws .9 turn out on one and .7 the other for perfectly acceptable idle and off idle response that I've enjoyed couple months now. Float level are low so that could well starve top end mixture.

Dang it. This logically means I must risk flooding again and harden heart to test if surge upset is reduced or eliminated. Trixie is so fine a ride as is - its mostly academic >>> as
*Definitely Destructive* level operation to Max out like i mean. Definitely Dangerous to crash too as I didn't do much WOT cuts while full upright in opens. Can ya feel the sensations, diving into easy sweepers feeling the pull top out in 3rd then snicking top pulling past a ton pressing just short of escalating THE Hinge by countering body efforts, to come out of blind straightening up WOT for traffic dead ahead - cut throttle for instant of relief then next instant smacked up back of head by spinal shock d/t fish like spasm off the deck Whoohooo SHIT. This what disappointed most, than lack of power, that let offs even essentially upright did not settle THE HInge but every little wind eddie and road texture and seeming pilot help just continued to magnify till a second or two had slowed enough it finally did. Too much for me ever again on un-tammed anything.

Will report back on changes, after a time.