Auto Technologies Head swap frustration

HI Everyone
My original combat cylinder head had been skimmed twice and the barrel once. To raise things up a bit I used a copper gasket etc etc, but would weep oil. To cut a long saga short, I decided to treat myself to the Auto Technologies cylinder head and duly swapped all the bits across into the new head and ground in the valves with paste as they were recently new anyway.
Took it out for a spin everything fine, but at 70mph bike became breathless and would not pull anymore in top. drop a gear to keep revs higher, still doesnt want to know.
I posted about this issue some months back and I have tried all suggestions. The Carbs are new Mk 1 Amals standard settings. Iv played with main jet, needle jet combinations and needle height. Tri- Spark ignition (a replaced unit) and new coils. Timed correctly.
As far as I can tell there are no air leaks around the carb to cylinder manifolds.
Valve clearances are as standard 8.thou inlet and 10 thou. exhaust. The bike is 1972 standard spec.
Am getting kinda worried it might be something more radical. Cos Im tired of removing the head again!!
Im not suggesting there is anything wrong with the new head, but nlowering the compression seems to have changed something?? With the original head,apart from the leaks the bike ran fine.
Any further thoughts will be much appreciated. Thanks

Did you fit the new amals or adjust the timing at the same time or since fitting the head?

Try checking cylinder pressure, though the usuall causes of many for refusal to rev can be cam timing, ignition advance too much or too little. The petrol now at the pumps is very poor. However I find Shell V max is not bad, even so I have had to retard my 850's ignition by 3 degs to get her to run well. (9.5 : 1 and 3S cam)

Cash

Hi Folks.
I had fitted carbs and ignition before changing to the new head. Bike was running very well. Was hoping it would be a straight forward head swap!! Have also timed the bike using a disc to the camshaft.
Obviously compression has been reduced with a higher head rather than the skimmed combat head, which keeps bringing me back to carburation, but have tried most things except for a different spray tube. Presently have one without the cutaway.
The exhaust porting is different to the orignal head and I have Interstate pipes and silencer. Im straw clutching here, but I wonder whether the gases are escaping effectivly??? Mmm Unlikely eh!
Im back to using the original standard pushrods also and no apparent problems with valve clearence adjustments.
Keep the ideas coming please!!!

Cheers

Aries

The new head has more efficient ports and you have lowered the CR. My thought is that the carbs are experiencing a much different signal; part of me thinks a lesser and part of me thinks greater and I'd be inclined to start varying the size of the main jet. You mentioned that you had played with the main jet; what did you try; any plug checks?

The standard Combat came with 220 mains, Id try a set of 210s and a set of 230s and see which direction yields the best results then expolit that direction; leave the needle out of it for the time being and concentrate on WOT.

RS

A PS:

The Combat has 32mm carbs and manifolds, how do they interface with the new head?

RS

If the new head is 30mm intakes, then there are 32 to 30mm manifolds out there part number 065196. There was a set on ebey that did not sell, 250756801136. Another option is to open the carb side of 30mm manifold to taper a bit to releave the ridge.

i can guarantee the 32 mm manifold mating to a 30 mm smaller port that leaves a lip to trip up flow turbulence sure put some extra kick in Ms Peel -especially in the upper rpms beyond 70 mph. I had great disappointment in power after stuck throttle event that stopped power increase at 4900-5000 rpm - 110 mph. I later found that the cam tensioner had failed so apparently the Boyer was over advancing - plus also found one exhaust lobe flattened. Not likely your poop out issue.

i assume FullAuto head flows more air than stock heads at higher rpm so makes sense to enrich the mix as next test. Maybe play with the spark timing up and down too.

hobot said:

i can guarantee the 32 mm manifold mating to a 30 mm smaller port that leaves a lip to trip up flow turbulence sure put some extra kick in Ms Peel

Click to expand...

I know that it is suggested that a rough surface is good and that polishing can be a bad thing, but are you saying that the lip on either a 32mm carb on a 30mm manifold or a 32mm manifold to a 30mm intake is a good thing?
And in addition, 30mm heat insulators at the head of all our combats going to give us "some extra kick"? Is that what you're saying?
And just what is "extra kick"?

If you were suffering that much fuel starvation at 70 and tried to keep the bike going wouldn't the lean condition show in the head pipes bluing rather fast? I ask because I had the same thing happen on a trident. At 70 it just ran out of power, gas literally, but the pipes blued fast.

When reducing the compression ratio with the new head you will reduce the signal to the carb that draws the fuel from the jet. Therefore you will need to go considerably larger on the mainjet. You may also need to go larger with the needle jet as it may be resrticting the fuel at full throttle. Changing the needle shroud should not be needed.

The full auto head has 32mm ports at the flange. Exhaust flow will not be a problem as the new exhaust ports flow more than the originals. The step in the floor of the exhaust will block some of the reversion wave that comes back from an open exhaust and may require small changes in the lower throttle settings such as pilot jet and slide cutaway. Jim

Aries, how good is the fuel flow from the pedcocks. Do you have 1/4" of 5/16" fuel lines? Are you running the old "H" configuration or the straight through method with the fuel lines. Just a thought.

i'm saying Ms Peel Combat head got lost for 1.5 yr after sent to M.A.P. cycle, whoos head shop quite doing heads w/o returning head to MAP or owners. So to get Peel new engine broken it I stuck on a bone stock standard 750 head and scabbed on 34 mm Miki carb with 32 mm one-two manifold and very crude thick rubber gasket that protruded ragged edges into air stream at the miss~matched mating lip. Then for 1000 miles i took it easy working up throttle loads and rpm till time to really see if I'd build engine to take red line WOT, WOOOWEEE what a shock I got as bike would run out from under me w/o serious butt planting and bar gripping FIRST before snapping throttle and did not stop the strong pull to at least 130 mph, though speedo rose and bike pulled beyond that to show 135 any time I cared except short steep climbs. Even there kept hunting for 5th to slow up the sensitive throttle response climbing beyond legal speeds into blinds a cop could be lurking, to be surprised I was in top already.

Then put on dual Amals with matched manifolds and power dropped, then got back CHO head with Dreer's 6 mm valve/spring kit, and power dropped to below ordinary Combat and had to stop hunting down hi fluting sport bike hot shots. Then had stuck throttle damage [11,000+ rpm] before I got to put back in original mere break in accidental set up.

So I don't know what your issue is or if a gain by streamlining air path will help of hurt or do nothing. I only know there are improvements in other engines by lips and texture-ridging surfaces for more turbulence. Also smaller ports often work a treat below pure red line flow rates.

One other thought - exhaust tuning made another big bump in Peels power via a 2-1-mega, but don't know how to advice you- as dual peashooters pretty good across power band as is. Peel headers were 1.5" size.

One strange comment I see on FullAuto head is most the power increase is low to mid range, but not as much or any near top end, so confused as usual. If you do find the solution to bogged power we may all learn useful insights.

May check your muffles / exhaust system for blockage. I tried a set of new mufflers on my bike and it would not run very well at all untill I knocked the baffels out of them.

Hm, yeah Peel woke up most after I shot out big hole in mega baffle plate and also my SV got deeper note than ATV 4 wheeler when I shot out two 38. cal holes in its factory baffle plate for a detectable pick up in low to mid range response. I sense a fundamental discovery lurking when this case of dull performance is cleared up.

Hobot, curious what was your super charger boost set at all those times when you were easily hitting 135mph?

Of course, I assume that your Druin was hooked up and dialed in perfectly because no way in hell your single Mikuni would flow enough without
the super charger to get anywhere near these incredible top speeds you constantly post about.

Aries,
May I ask if one of your checks included how it reponded to slowly dropping the choke?

The easy way to quickly sort out this type of problem is to find someone with a rolling road dyno, who knows what they are doing and run the bike on the rollers. Otherwise its very easy to spend a great deal of time messing about with things that might not have anything to do with whats actually wrong.

Hehe, I don't give a flying flip what you falsely accuse me of, I've got my memories in my bones that constantly flash on me 24/7, especially when traveling same routes in my car while all my cycles dead in my shed. I know what i had and want more of it, sorry if you can't believe what you are missing out on. Shocked me too, but now I'm hopelessly addicted. My message as always is you too can have what I did w/o breaking the bank or being race skilled rider w/o a blower, as enough G's in turns hi horse power was useless to catch up in time, Yeehaaww. I repeat Ms Peel in her accidental set up Never Got Passed in tests I begged them to match speed to compare speedo readings. I got out dragged in take offs and in opens before hitting top end and in places I just couldn't face blinds I let the squids zoom past. Spread as much BS as you like, I remain pissed off no one would match Peel's top end even if they could easy, they just wouldn't, so laugh at me all ya like, you are not my enemy, nor in the league of the class of cycles I've got my sights set n to embarrass.

I long to hear of others having even better blast than me, but doubt anyone will once my lightened up linked isolastic supercharged big block comes on line. If not for the excessive handling security a Combat with Drouin would be way more than I could handle. Hope you try my suggestions someday then get back to us.

i await the tuning secrets that bring out the best in FullAuto heads.
Day off mild temps so off to assemble plain Jane Trixie Combat that behaves exactly as everyone else and likely a bit worse, but still a delight as long as not trying to follow moderns or vintage racers.

"When the flag drops the BS stops" is perhaps something certain posters on here need to bear in mind?

Carbonfiber, I"m not mad at you for challenging me, as I said Peel was so freaking good it made sports bikers angry at me to ask to tag along, so much so it gradually became part of my hobby to seek this out and then have it out. I see Old Brits has a dyno, so want someday to send them two engines, one set up as accidental 'against the grain' past 750 Peel and current 920 engine thats almost done. Big block is only to take on the big dawgs at least to 1/3 over tire ratings.

I wonder if a FullAtuo head might be worth extra power or just too much for me and Peel. Would be educational to send a FullAtuo head to try on dyno of the 2 engines. Trouble is on 920 the head must be milled out wider for the pistons to stick up into, so don't expect to have money enough to commit to that.