Topic: 76 550 top gear rev problem

[FIREBLADE74]

Need help! I've searched but no one ever comes  back with a solution.

The bike will redline in all gears except 5th. It'll climb but stop at 5500, 75mph. The throttle is at the stop. Plugs go from white to tan across the cylinders with 1-3 white and 4 tan. The sync is spot on air screw is out 1.5 turns. I'm thinking the boots to the cylinders are shot, I did the starter fluid test.

Do y'all think the worn boots are causing this? I've ordered new boots but want to make sure I'm not missing anything.

Bike is a 550ss with 6100 miles.
3k service done.
Point gapped and timing set.
New plugs
Pod filters
110 main jet

[Bodi]

Worn boots would cause lean mixture. Vacuum is lowest (manifold pressure highest) at WOT so that's unlikely to be your problem. What speed is it going at 4th gear redline?
It should easily top 75mph in top gear but none of the stock fours will pull redline in top gear unless going downhill with a stiff tailwind.

[BomberMann650]

Yeah, it's a lot easier to do the ton if you've redline shifted in 4th.  Which is about 85mph ish

[FIREBLADE74]

Bet! What I noticed is that if I redline 4th, I can get 5th over 6rpm barely tho.

So these bikes can't really redline 5th easily?

Thanks guys, ill hit back what the new boots do.

[FIREBLADE74]

Worn boots would cause lean mixture. Vacuum is lowest (manifold pressure highest) at WOT so that's unlikely to be your problem. What speed is it going at 4th gear redline?
It should easily top 75mph in top gear but none of the stock fours will pull redline in top gear unless going downhill with a stiff tailwind.

Didn't notice the speed, ill say about 60-65.

[BomberMann650]

Make no mistake, the cb550 can and will go to the max when it's tuned and running properly.  I've noticed a bit of a character change since switching to a pamco ignition timing unit (with a clean and lubed advancer unit).  Which as made it easier to roll on the throttle in 5th and do the boogie.

Things that have slowed me down are,
1) unsynced carbs
2) points timing wrong
3) valve tappets out of spec
4) fuel mix wrong (both float level and a/f screw)
5) brake drag (didn't adjust the rear brake screw when changing tires)

And a big one that I battled EXHAUST LEAKS and an airbox seal leak.

[FIREBLADE74]

Make no mistake, the cb550 can and will go to the max when it's tuned and running properly.  I've noticed a bit of a character change since switching to a pamco ignition timing unit (with a clean and lubed advancer unit).  Which as made it easier to roll on the throttle in 5th and do the boogie.

Things that have slowed me down are,
1) unsynced carbs
2) points timing wrong
3) valve tappets out of spec
4) fuel mix wrong (both float level and a/f screw)
5) brake drag (didn't adjust the rear brake screw when changing tires)

And a big one that I battled EXHAUST LEAKS and an airbox seal leak.

I'm betting all on the rubber boots being dry rotted.

Lubing advance unit? Is that pamco specific?

[BomberMann650]

A clean advancer unit is something everyone should have. 

Alas, the pamco instructions did have a prompt.

[calj737]

I'm betting all on the rubber boots being dry rotted.

I'll take that bet. I'll bet you your fuel level/mixture is wrong and you are starving for fuel at the higher speeds. Supple boots will help in all areas, but if they were the source of your issue, the issue would be very noticeable at idle.

[FIREBLADE74]

I'm betting all on the rubber boots being dry rotted.

I'll take that bet. I'll bet you your fuel level/mixture is wrong and you are starving for fuel at the higher speeds. Supple boots will help in all areas, but if they were the source of your issue, the issue would be very noticeable at idle.

What would be noticeable at because my idle isn't the best, lol.

[FIREBLADE74]

Ok the boots wasn't the problem but I noticed if I get 4th up to about 7rpm before I shift I can get 5th to creep pass 6rpm.

Coming from a 1kcc bike I may be expecting too much. Am I?

[DaveBarbier]

Ok the boots wasn't the problem but I noticed if I get 4th up to about 7rpm before I shift I can get 5th to creep pass 6rpm.

Coming from a 1kcc bike I may be expecting too much. Am I?

Are you riding with a 4x8 sheet of plywood facing the wind?

You should be able to go higher in the revs in top gear. On my 550 I can go around 8k in full tuck slightly uphill on this stretch of highway where there's no cops

[FIREBLADE74]

Ok the boots wasn't the problem but I noticed if I get 4th up to about 7rpm before I shift I can get 5th to creep pass 6rpm.

Coming from a 1kcc bike I may be expecting too much. Am I?

Are you riding with a 4x8 sheet of plywood facing the wind?

You should be able to go higher in the revs in top gear. On my 550 I can go around 8k in full tuck slightly uphill on this stretch of highway where there's no cops

Lol, feels like it!

[FIREBLADE74]

Ok played with the air mixture:

1.5 turns grayish white
2 turns bone white
1 turn dry black

1.25 should be the sweet spot

[jonda500]

So going by that turning the airscrews in definitely made it richer and turning them out made it leaner - do you have any pics to back that up so we can put the airscrew debate to bed forever?
John

[FIREBLADE74]

So going by that turning the airscrews in definitely made it richer and turning them out made it leaner - do you have any pics to back that up so we can put the airscrew debate to bed forever?
John

No pics but righty is rich and lefty is lean.

1.25 turns is not the sweet spot! SMFH!

The kicker is it hauls azz in gears 1-4, but fall flat in 5th.

I'm now thinking my spark maybe weak. I do still have the coils from 1976 on there. What do you guys think?

[DaveBarbier]

So going by that turning the airscrews in definitely made it richer and turning them out made it leaner - do you have any pics to back that up so we can put the airscrew debate to bed forever?
John

No pics but righty is rich and lefty is lean.

1.25 turns is not the sweet spot! SMFH!

The kicker is it hauls azz in gears 1-4, but fall flat in 5th.

I'm now thinking my spark maybe weak. I do still have the coils from 1976 on there. What do you guys think?

I would test them first. I think there's info on how to test in the FAQ. If the coils were bad you wouldn't haul a$$ 1st-4th. I think it's pretty rare for the coils to go bad, they're pretty robust units. Mine from '78 perform fine. My other bikes I've had from '74 were the same.

Here is the coil testing info from the FAQ:
http://forums.sohc4.net/index.php/topic,5752.msg8383.html#msg8383

I'd focus on carbs. Remove and clean them and check fuel level with clear tube method.

Tire pressure good? Doubt that has anything to do with it but hell, thought I'd ask.

[FIREBLADE74]

So going by that turning the airscrews in definitely made it richer and turning them out made it leaner - do you have any pics to back that up so we can put the airscrew debate to bed forever?
John

No pics but righty is rich and lefty is lean.

1.25 turns is not the sweet spot! SMFH!

The kicker is it hauls azz in gears 1-4, but fall flat in 5th.

I'm now thinking my spark maybe weak. I do still have the coils from 1976 on there. What do you guys think?

I would test them first. I think there's info on how to test in the FAQ. If the coils were bad you wouldn't haul a$$ 1st-4th. I think it's pretty rare for the coils to go bad, they're pretty robust units. Mine from '78 perform fine. My other bikes I've had from '74 were the same.

Here is the coil testing info from the FAQ:
http://forums.sohc4.net/index.php/topic,5752.msg8383.html#msg8383

I'd focus on carbs. Remove and clean them and check fuel level with clear tube method.

Tire pressure good? Doubt that has anything to do with it but hell, thought I'd ask.

Damn those carbs! I'm going to take them somewhere to be professionally cleaned!! I've cleaned those carbs about 4 times now, but I think that's my problem! I'm going to tear them down to their very last compound, lol.

But if it were the carbs wouldn't the problem be noticed in every gear?

Tire pressure at 36.

[calj737]

But if it were the carbs wouldn't the problem be noticed in every gear?

Yes.

[DaveBarbier]

But if it were the carbs wouldn't the problem be noticed in every gear?

Yes.

Ah, so Cal are you suggesting more like fuel delivery like clogged tank vent or inline filter?

[FIREBLADE74]

But if it were the carbs wouldn't the problem be noticed in every gear?

Yes.

Ah, so Cal are you suggesting more like fuel delivery like clogged tank vent or inline filter?

No inline filters so I'll check the breather tube and try riding it with the gas cap open.

[calj737]

I'm betting all on the rubber boots being dry rotted.

I'll take that bet.

Ok the boots wasn't the problem

Sucks being right.

[FIREBLADE74]

I'm betting all on the rubber boots being dry rotted.

I'll take that bet.

Ok the boots wasn't the problem

Sucks being right.

Damn calj lol.

[FIREBLADE74]

This is my kinda chop, 3rd gear 8krpm, 60-65mph.

Plugs 1, they all look the same. I cant seem to load anymore

[FIREBLADE74]

plug 2