Topic: when did the emmissions laws slow the performance of these bikes?

[mrblasty]

A few of You guys have said that at some point emissions laws have slowed these bikes down.  What year did this begin to happen and what was done to "detune" the motors.

[Cvillechopper]

I'm not sure I've read about the emmission laws slowing down the bikes, but in 77 the 750 carbs began their move toward a less easily modifiable set-up.  They changed the needles so they were not adjustable and in 78 they used press-in slow jets.  The idea was that you should use the STOCK setup and leave well enough alone.  I've got mine as modified as can be (78 cb750K) and it was not very easy to find larger jets and even when I did, I still don't have her quite right.  Maybe someone else knows if the mods make performance decline on the olders SOHCs but everything I've read indicates improved performance if you have stock set-up. 

[bistromath]

I believe they leaned out later 750's to reduce emissions, but I'm not a 750 guru.

[Jonesy]

1973 is usually pegged as the year when stuff started to happen. On the K3 750 the airbox had smaller intakes (reduced intake noise), More extensive baffling in the mufflers (again less noise). These restrictions called for rejetting from the original 120 main to a 110 briefly, then down to a 105. The K0 had a hotter cam and higher redline, both of which were scaled back on the K1. In either the K6 or K7 models the breather for the crankcase was routed to a small vapor canister under the battery, rather than the open air for hydrocarbon emission reduction. I think it was around this time as well that small plastic limiter caps were put on the idle air screws to keep us regular folk from fiddling with them and polluting the air more than we had to.

[mrblasty]

Thanks folks, thats what I was looking for.

[theunrulychef]

I was just trying to figure out how to move the position of my needles on my 77 cb750f the other day.  WTF am I supposed to do now?  Do I actually have to go purchase an older set of carbs to be able to get my bike running correctly, or can I just get adjustable needles? If not, half of the crap I've been reading about for my carb rebuild research is basically useless.  Please tell me there's an easy, cheap solution.

[oldfart]

Emissons laws, which for motorcycles began in January of 1978, have actually had much less effect on motorcycle performance as have other considerations related to consumerism.  Before 78, there were some things bike manufacturers did that addressed emission, but little of it had any effect on performance.  Things such as crankcase recirculation, for example.  However, driveability concerns and costs of production have dealt a much harder blow to motorcycle performance, even today, than has emissions.  Emissions laws have had much more effect on the manufacturer, specifically during the certificaion stage of vehicle production, and this in terms of will the vehicle pollute under any circumstances, at any time in its useful life, no matter how many examples of the particular vehicle are produced.  It is this last point that made carburetors so messed up during the late 70s and early 80s.  Go here for a more thorough treatment on that subject.  http://www.motorcycleproject.com/motorcycle/text/newcarbs01intro.html    :-)

   

[eldar]

Well chef, you would need to let us know what you have done. generally the f models came with a 4 - 1 for 77 and 78 I think. So unless you added pods which many are finding out kinda suck, or run a K&N filter, you should not need to do anything with the needles.  Make sure you have proper adjustment on the valves and that timing is correct. Then so your sync and low speed mix adjustment. These are where the biggest problems occur. Not the main needles. You also do not say if you are rich or lean.

[theunrulychef]

77 CB750F2
Eldar, I've replaced the stock 4-1 system with a stock 4-1 header & a Carpy special slip on (shotgun) - stock airbox.  Boyer digital ignition, timing at idle is spot on (advance still not quite to the marks even though the plate is all the way over).  I've completely rewired a few select ignition wires that looked dodgy & redone all the connections on everything with spades & dialectic grease. Still trying to get that one stuck f'ing tappet cover off so I can check all the valve clearances (haven't done the others bc I wanted to wait until I got the new covers in the mail - arrived yesterday). Cam chain tension is good.

I noticed before I switched the exhaust that the bike was running rough & when I had the headers off, they had alot of black soot inside.  I figured I was running rich.  The overall performance has increased; pulling power up, throttle response is much better when warm.  Plus it has a wonderful sound.  I figured that with the new pipes, with the performace, I probably wouldn't have to rejet.  Then I started having problems.  It was popping on decel, and now that's turned into popping on idle too & idling rough. 

Pulled the carbs & cleaned out the mains & reset float height. I was working off of a 78 manual which said that the slow jets were pressed in so I didn't mess with them. Now I realize that with my 77 carbs, I should at least be able to pull them & clean them out.

I've rechecked & rechecked timing & cam chain tension.

To my surprise, I couldn't get the airbox open, as the last people who had it out was my local stealership - they overtightened one of the bolts & now the nut inside just spins & spins.  I looked in as well as I could & it seemed the air filter looks clean enough for right now. While I was poking around, I reset the throttle cable  tensions (response is much smoother now).

Unfortunately for my bike, I live in Philadelphia.  That means I spend as much time sitting at stop lights on idle as I do riding.  Not only that, there's NOWHERE nearby for me to do a plug chop.  One time, I'll pull my plugs & they look like I'm running rich, another time, they look like I'm running lean. Currently, it's pretty difficult for me to figure out whether I'm running rich or not.

To top it all off, I've been messing around with my gasoline grade.  I used to use 91.  Then I read that it will actually create more carbon deposits in my bike, so I switched to 89, then 87.  This is all within the past month that I've been having problems.

I've got some parts & a carb sync gauge coming in the mail.  I'm planning on having a "session" with the beast this weekend - valve clearance, clean the slows, carb balance, new plugs & figure out something with that damned airbox.

From what I've read, here's a FEW of the problems I think it could be:
Low/Dying Battery
Incorrect Jet Size
Vacuum Leak on intake somewhere
Exhaust Leak (getting new gaskets)
Bad Plugs (replacing plugs)
Bad Wires or Coils
The Jebus hates me

Sorry for my incoherrent ramblings.  I haven't had enough coffee yet & it's hard to remember all the tweaks & "try this" moments I've had with bike.  I know I'm not working in the correct service order (far from it), but hopefully this weekend, I can change all that & possibly start up my own thread once I've finally checked all the usual suspects.

Thanks,
Jay in Philly

[dusterdude]

jay,i wouldnt say you were incoherent,however eldar may think so because he is a k8 man,and you know how intelligent them k8 guys are.

[eldar]

Now duster, try not to be too sore!    We all play our own hands in life, some are just lucky enough to get a hand winning K8!

ok enough of that, well for now anyways!

When you changed exhaust, you changed your baffling and backpressure. See your old muffler would be worn and have less baffle and thus less back pressure. over time tune-ups compensate for this and when you put on a new system, things can run like crap. The popping is usually from unburnt fuel in the exhaust. I dont know about the carpy special though. 

Technically you can do a plug chop at any rpm, the thing is you need to be at certain rpm to test certain ranges.
So you could test your idle circuit by idling and then checking the plugs.

For the airbox, is it a stock filter?  As for the bolt, that was done on my bike by the PO. A nut was welded on to  allow the airbox to be split.  You CAN remove the airbox in one unit but it is a pain but this will allow you to bet at the nut to either get it off or weld one on.

you can pull out the low jets, do not wiggle them just twist. Clean them if needed but you should not have to replace them with other sizes. I also suggest running a can of seafoam through the tank, not a whole can just 1/3 to 1/2.

If you got new valve covers, then get that old one off however you can. If you have all these small things like stuck covers and striped bolts and such, then the previous work on the bike might be poor, that happens with POs.

[dusterdude]

 

[theunrulychef]

Thanks for the tips. I'll have to check my local parts house or marine shop for the Seafoam conditioner.

The new muffler has pretty much no baffling - just a little on the sides with some packing.  It's a straight shot through, so I can't imagine it would have less back pressure than the old stock cannon that was on before.   Here's a link to a pick of Carpy's exhaust mod (Here).  I was figuring that the loss of back pressure would give me a little roughness & torque loss on the low end, but it could still be tuned much better than it is at present.

I was thinking, almost hoping, that the popping would be from running rich, but it's been hard to tell exactly what's going on since I'm obviously pretty inexperienced with bikes & I didn't even think I could do a good plug chop.  It's good to know that the bike doesn't have to be running under load to do it correctly.  I'll make sure & do that this weekend when I dig in with the tune-up.

Yeah the air filter is stock.  It's been a pain to get it in & out as a whole piece, but a little grease on the boots helps it to slide past the carb intakes.  I'll check out the housing again to see if I can't fix it.  It seems like the nut is spinning inside the housing, not the one on the bottom.  I'll have to figure out how to get a hold of the damned thing from the outside & crack it open w/o breaking it.  I'm sure I should blow out the air filter if nothing else.  I know alot of people don't like them, but if I moved to the dreaded pod filters, wouldn't that lean out my seemingly rich condition? (using my own shovel to dig my grave on that one  )

The stuck valve clearance cover is going to be a #$%* - I might have to pull out the torch because it hasn't budged with light hammering, penetrant, pliers, & finally the always irresponsible vise grips.  Sucks that I can't drill it out - I doubt the engine would like all those aluminum shavings.  If nothing else works, I guess I could move to the punches & chisels.

Thanks again for the help. 

-Jay in Philly

ps - I know I can't use the coffee excuse for my post this time as it's the middle of the afternoon.

[eldar]

Well for the filter, it is more than likely that it is the bottom nut that is spinning. If it was the top, then that would mean the bolt broke and you should be able to just pull the housing apart.

For low speed you do not need to be under load, but for higher rpm you do since you want to run for a couple of minutes at the high rpm.

Pods do not deliver consistent airflow to all the carbs all the time. they also kill midrange and I thinks lows. They are mainly high speed items and with what you describe about PA. High speed does not happen much.

If you have it, you could try an air operated impact hammer set to lower pressure to get the cap off.

[TwoTired]

I was thinking, almost hoping, that the popping would be from running rich, but it's been hard to tell exactly what's going on since I'm obviously pretty inexperienced with bikes & I didn't even think I could do a good plug chop. It's good to know that the bike doesn't have to be running under load to do it correctly. I'll make sure & do that this weekend when I dig in with the tune-up.

I think you'll find that loading has a pronounced effect on mixture requirements.  Doing plug chop tests and adjustments in your garage with no load will make it run really well in the garage.  However, it will likely be totally lacking for power on the street.  Further, the combustion temps at idle speeds don't really clean off the plug deposits well enough for reliable readings.  This is why successful tuners use a track and stopwatch or a Dyno for jetting their carbs.

The stuck valve clearance cover is going to be a #$%* - I might have to pull out the torch because it hasn't budged with light hammering, penetrant, pliers, & finally the always irresponsible vise grips. Sucks that I can't drill it out - I doubt the engine would like all those aluminum shavings. If nothing else works, I guess I could move to the punches & chisels.

You want to save the big valve cover, not the small one.  A torch will expand metal and remove paint.  You might try going to an electronics supply store and find cold or freeze spray.  This will freeze the small cover, shrinking it a bit, and perhaps allow it to release its grip on the large cover.  For extremes, you could warm the engine first to heat the big cover, then freeze the small one, then smack it with chisel, hammer, whatever.

[eldar]

You can do a low speed chop in the garage. If you clean the plug very well then run it, it can still give a good indication of low speed mix. This may not work on the earlier 750s but it does on the 77 - 78. If you run for a few minutes, the plug WILL reflect the running nature of the engine if it is lean or rich. It may not be quite as accurate but will still allow a good low speed adjustment.  It will not work for higher speed though.  I have done this with positive results and I am sure any one could. Nothing takes the place of a good dwell/tach but those are not the easiest to find anymore. And not everyone is a racer or has a track. Some areas do not even HAVE tracks.

[Bob Wessner]

It works fine on the earlier 750's as well. This is where I started. The only thing I would recommend is that you make sure the engine is thuroughly warmed-up, a fan blowing on the engine wouldn't be a bad idea either. For the next step, I took it out for low speed riding around the neighborhood, rechecking, and finally you do the cruising check that is more likely to include needle adjustment if necessary. So far though, the middle position on the main needles seem to be just about right.

[theunrulychef]

I guess I'll just have to bite the bullet & go out in the sticks somewhere with a plug wrench to check my midrange & WOT settings. Anything else I should bring along with me for a test like that?

I'll definately look at my low speed plug condition this weekend since that's where most of my problems lie.  I'm still getting a little stumble here or there when I decide to do a WOT, but generally once the bike has had ample time to warm up it's not a problem (& I don't really ever need to do WOT).

I've been tweaking 1/8 turn this way , 1/4 turn that way with the idle adjustments, but it seems to be pretty darn hard to find the sweet spot w/o a shop tach (did see a couple on ebay for around $20). I think after all of the stuff I'm doing this weekend, I'll hopefully at least narrowed down most of my other problems.  Then a good idle air session & a carb sync perhaps will get her purring.

Unfortunately, it's the #3 intake cover that's buggered.  It's a good point about not messing up the main valve cover though.  I am planning on pulling it one of these days & stripping the black off (not really looking forward to that).  Perhaps if I warm the engine up, then rub ice cubes on the cover to make it cool faster?  I'll also take a look to see if I can't find the freeze spray over at Radio Hack.

The airbox bolt is strange.  I turn the bolt on the top, and I can feel something inside popping past the plastic, but the nut on the bottom isn't moving.  It's been about a year since I personally was in there (not since the last air filter change) & I can't remember how everything is put together to visualize what's happening.  I'll have to pull out the manual for a diagram.  I guess I can always find one on ebay from someone that's switched over to pods.

Back to the needle height though.  If was to lose power in the midrange, or run too rich, how would someone fix that with these carbs?  I'm not someone that really wants to have everything bone stock - I like to tinker (isn't it obvious).  Am I basically SOL when it comes to needle height, as it seems many people here on these forums get to play fair with their carbs?

Now I feel like I have the redheaded stepchild carbs.... makes me want to beat them more.

Thanks again for everyone's help. 
-Jay

[eldar]

Well if you go to do a test like that, bring a phone! Otherwise a small assortment of the most common tools, philips, 10 - 17 mm sockets or wrenches. Some electrical tape, fire extinguisher......

Your high speed stumble could be anything and not even have anything to do with the carbs. the points may need service or #3 intake may be off, it is hard to say. Thats why you want to do the basics before goofing with the carbs.

As for a shop tach, if you are still using the points, get a dwell/tach meter. the tach is electrical and very accurate and the dwell will help you set the points dead on.

With the airbox on my 78, The nut on the bottom is not just a nut. It is a tube with a hex head end that the top bolt screws into. Yours should be very similar I would think. If the top keeps spinning and the bottom does not move, then I would say that somehow the threads  got boogered up. You will need to pull the airbox and as you are trying to unscrew it, try pulling it apart at the same time. this may allow enough bite on the threads to unscrew it or else the halves whould pull apart. Then you will need to get new bolts for the box.

You are not likely to run too rich with these carbs except in low range. The low speed jets do affect the mid range too some what. You may have to pull the jets and use a wire to make sure they are fully clean.
I would not want the have the earlier carbs myself. These are just as tuneable, the methods are just a bit different. If you have the 77 carbs, your needles should have clip grooves that can be used to move the needle up or down. These carbs are just as good as the others. We can use different mains and even low speed screw ins. Just ask buffo. He did it I think.