Topic: A Little More

[spiritof67]

I am looking for a way to get just a little more power from my K1. I have access to another cylinder head and a set of accelerator-pump carbs. Would just headwork and a cam with the carbs give me what I am looking for?

[PeWe]

You need pistons with higher compression and deeper valve pockets to use a hotter cam which has higher lift and longer duration.

Stock K carbs will work fine with ev 836, hotter cam, ported head.

When porting, the guides and valves are probably in need of replacement which brings cutting the seats.

Check with forum member MRieck that port heads and do what needed to improve the engine. Hopefully not retired yet

[MRieck]

Check with forum member MRieck that port heads and do what needed to improve the engine. Hopefully not retired yet

Retired from my old day job Per.....not porting.

[Stev-o]

I would suggest an 836 kit, I have Wiseco's on my K4.

It will pull away from a stock 736cc bike...

[gschuld]

Question 1. How healthy is your current engine.  As in, is the compression even across the cylinders?  Are the factory carbs in good shape?  Does it idle well? Does it pull away smoothly?  Any significant chain noises? Shifting Ok?  Mileage?

I ask because if you have a really healthy current engine as is, considering a modest ported head/cam/springs upgrade and leaving your rotating assembly and carbs stock will be well worth considering since it is a more limited project(in effort and cost)

Factory round tops EASILY handle 80 RWHP at 736-762cc.  We have factory carb restricted road racers that have proven that.(dyno proven)

If you stick with the factory rotating assembly/bottom end, you’d want to find out how much you can get out of the top end without interfering with your OEM pistons as is.  Is really valve to valve pocket clearance at issue.  You can deck a head to increase compression a bit, but that brings the valves closer to the pistons. Then throw a larger cam in and the valves get closer still.  My guess is you can get a little more compression, 33.5/28 or 34/28 valves, some nice porting, and a mid range cam and make a very noticeable improvement over stock.  You won’t want to drag race any modern sportbikes however.

Mike Rieck is your man IMHO.

If your engine is higher mileage or making a bunch of questionable sounds, uneven compression, etc, then it’s time to consider other options(usually more involved, more expensive options).
A cast 10:1 compression 836 piston kit, bored factor cylinders, head, cam, springs, etc on a fresh rebuild on the rest an you can have a nice running engine that could last you a good long time.

Consider how you use the bike.  If you are into multi day long road trips where far away from home reliability is super important, that would be a factor.

Rob, Voxonda, has endurance road raced with a dead stock factory bottom end, with only cam, ported head, aftermarket exhaust being the extent of his mods.  He has also built top to bottom race engines.

There are options.  Much depends on what you have currently, how much extra power you are shooting for, and your personal ratio of cost per HP(smiles) justifications.


George

[seanbarney41]

I have a K6 motored K5 that has stock .030 over pistons, F2 cam  (purported to be hottest oem grind) and self cleaned up ports with stock carbs and good intake and exhaust...I have not had it on a dyno but seems noticeably more potent top end than other stock k's and F0/1's I have ridden.  Good running F2/3  I had would beat it I believe.  Not very scientific but hopefully might give you some perspective on what might be done for very low bucks and effort.  Differences for you?!...K1 cylinder head should be much better than K6, so it is gonna be harder to for a diy'er to realize gains.  And if you value low end torque, proceed with caution.  Cb750 doesn't have much to start with and many performance mods only really see gains at higher rpm.

[MRieck]

Question 1. How healthy is your current engine.  As in, is the compression even across the cylinders?  Are the factory carbs in good shape?  Does it idle well? Does it pull away smoothly?  Any significant chain noises? Shifting Ok?  Mileage?

I ask because if you have a really healthy current engine as is, considering a modest ported head/cam/springs upgrade and leaving your rotating assembly and carbs stock will be well worth considering since it is a more limited project(in effort and cost)

Factory round tops EASILY handle 80 RWHP at 736-762cc.  We have factory carb restricted road racers that have proven that.(dyno proven)

If you stick with the factory rotating assembly/bottom end, you’d want to find out how much you can get out of the top end without interfering with your OEM pistons as is.  Is really valve to valve pocket clearance at issue.  You can deck a head to increase compression a bit, but that brings the valves closer to the pistons. Then throw a larger cam in and the valves get closer still.  My guess is you can get a little more compression, 33.5/28 or 34/28 valves, some nice porting, and a mid range cam and make a very noticeable improvement over stock.  You won’t want to drag race any modern sportbikes however.

Mike Rieck is your man IMHO.

If your engine is higher mileage or making a bunch of questionable sounds, uneven compression, etc, then it’s time to consider other options(usually more involved, more expensive options).
A cast 10:1 compression 836 piston kit, bored factor cylinders, head, cam, springs, etc on a fresh rebuild on the rest an you can have a nice running engine that could last you a good long time.

Consider how you use the bike.  If you are into multi day long road trips where far away from home reliability is super important, that would be a factor.

Rob, Voxonda, has endurance road raced with a dead stock factory bottom end, with only cam, ported head, aftermarket exhaust being the extent of his mods.  He has also built top to bottom race engines.

There are options.  Much depends on what you have currently, how much extra power you are shooting for, and your personal ratio of cost per HP(smiles) justifications.


George

Thanks George for the endorsement. It isn't that hard to get an extra 20 RWHP out of these engines.....I've done nit with AndyCB but I'll never work with those parts again.

[HondaMan]

Check with forum member MRieck that port heads and do what needed to improve the engine. Hopefully not retired yet

Retired from my old day job Per.....not porting.

Now, that's TRULY a loss!

[HondaMan]

I am looking for a way to get just a little more power from my K1. I have access to another cylinder head and a set of accelerator-pump carbs. Would just headwork and a cam with the carbs give me what I am looking for?

IMHO, you will be better off with the OEM carbs. The accelerator-pump (PD) carbs were made to provide emission controls, not increased performance.

I can recommend the cam #125-00 (0r #125-04 in hardweld) from Megacycle as a great start. For this one, the only carb 'change' needed is to turn the idle air screws inward toward 3/4 turn to make it idle nicely in city riding and ensure a smooth blend from takeoff to nominal run speeds. Some of the "hot" cams out there can make for tricky (nasty) city riding because of flat spots they can cause just off idle.

Higher compression is one way to perk it up, but I prefer to stay with cast pistons for longer life. Many high-compression pistons made for these engines today are forged instead of cast, so they have issues you will have to learn to live with, and shorter life than cast pistons due to the increased piston clearances needed for forged versions. In this route, you can use the -392- (F0/1, K7/8) or even the -410- (F2/3) type pistons in the earlier engines, although you may have to slightly modify the combustion chambers to ensure they clear the domes (especially on the F2/3 type pistons).

Going to 836cc will increase low-end torque from the extra cc displacement, while the Megacycle cam will increase the power at higher RPM with all the pistons. Don't fret too much over the exhaust system you choose, as the pipes are all too short (except for the old Dunstall 4-2 system) to make any useful header effect in these short bikes. Just pick some pipes you like. If you have the K1 jetting it will work as-is in the #657A/B carbs, and if you new pipes are more restrictive you will need to lift the needles 1 notch to ensure a smooth transition from idle to mainjet circuits.

[PeWe]

Check with forum member MRieck that port heads and do what needed to improve the engine. Hopefully not retired yet

Retired from my old day job Per.....not porting.

Now, that's TRULY a loss!

Not retired from porting
So no loss for this forum

An old head need to be refurbished anyway so open up the ports when replacing worn guides and valves not that much extra.

But as the other guys wrote. The status of the engine.

 Probably new chains with tensioners, crank bearings?, clutch etc.

As I have mentioned before. Not worn enough to take it apart and restore
vs
too worn to assemble and use.

This means replacement while there.
Reopen and redo will cost extra gaskets, oil etc if doing it home.

[gschuld]

Check with forum member MRieck that port heads and do what needed to improve the engine. Hopefully not retired yet

Retired from my old day job Per.....not porting.

Now, that's TRULY a loss!

I think you misunderstood. Mike has retired from a long career of dealing with actual children.  Now he can concentrate on all of us adult children…😉

Great for us, maybe less so for Mike’s sanity.

George

[PeWe]

Good that Mike still create his head art.
Ported head is nice to look at and touch....