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Discussion Starter #1
I've been having an issue with my 350 losing power at >3/4 throttle when under load. This means that I have no trouble touching redline when in neutral, but under load I can't really get above 6K RPM. If I'm accelerating from 0 and I give it WOT, the engine can cut out on me. At cruising speed I can't get above 60 or 65 mph... it kinds of stutters and feels maxed out. This is in comparison with my friend's 350, which has much greater pep when accelerating from a stop and no top speed issues.

The engine was rebuilt about 500 miles ago and is all within spec. 180 psi compression in both cylinders, clearances set, points set. I went through my carbs last summer and they are clean, diaphragms good, jetting stock. I am running the stock airbox/filters. When I had the bike apart during the rebuild I didn't notice anything weird with the wiring/electrical.

What would cause this sort of power problem at WOT? One thing I suspect is my shorty EMGO mufflers, which are basically straight through open pipes. But would this affect the top end of the RPM range? If not the pipes, should I be zeroing in on the electrical system or checking out my carbs?
 

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What color are the plugs?
 

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Are you able to swap in a stock exhaust or baffled muffler?
What's on your friends bike?
What carbs do you have and what's the float level set at?
Though your plugs don't say, may want to try a bigger secondary main... If you have 105 then try between 110 to 115?
Also how's your charging system?
 

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Discussion Starter #5
Hi doode,

I don't have any exhausts I can swap in. My friend's bike is fully stock and I tuned it up for him so besides his stock exhaust, our bikes are pretty much identical. I have the stock carbs on. I forget the measurement the floats are set to but when I had them apart, they were at spec. One thing that occurred to me is the possibility of carb air leak, either at the rubber tubes or the felt seals. But that would be more of a low-range problem, right? And if it is an upper RPM erange problem, I wouldn't really be able to test for those leaks except while riding.

Charging system is great. May try rejetting.
 

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Try closing the choke part way when it starts to miss. If it gets better with the choke on it's too lean.
 

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Discussion Starter #7
i will try that. One thing I'm hoping to rule out is whether this is caused by the exhaust, because I'm teetering on whether or not to purchase another set of mufflers. Will an open exhaust cause more of just a weird acceleration curve or could it be causing such a huge power deficiency like I'm experiencing?
 

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The exhaust you have definitely isn't helping. I'm sure a more stock exhaust setup would make a noticeable improvement
 

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Discussion Starter #9
I'm working on that as we speak but I'm having trouble finding mufflers that aren't just straight-through perforated baffle exhausts like the one I have now. Can you or someone on this site recommend an attractive, low-profile muffler set that you have firsthand experience with and know will work fine on these bikes? I need a new set anyway because my current ones are too loud, and if I can rule out my mufflers causing this performance issue, I'd feel a lot better :)
 

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Discussion Starter #13
Thanks for the replies guys. I think i may have found the issue, but maybe you could help confirm. Im running ngk br8eix iridium plugs and just found that the caps are 5k ohm resistor type. Are these plugs also resistor type? If so, would that be enough to cause running issues?

I think i may go with the emgo widemouth dunstall-style exhaust or some shorties. Not sure yet.
 

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I have a 2-1 exhaust I built for my 70 CL350 and I am using a muffler from an early 2000's Harley at the moment. I have two of these mufflers so With the baffle separator in place I get good throttle response. The other muffler is drilled out and there is noticeable throttle bogging. I"ll also say before I built this exhaust I ran vintage VW tips in the 2-2 exhaust. Throttle response was ok but topped out at 7,000 rpms. With the non drilled 2-1 muffler I can hit 10,500 rpms easy when deciding to push it.
 

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I have a 2-1 exhaust I built for my 70 CL350 and I am using a muffler from an early 2000's Harley at the moment. I have two of these mufflers so With the baffle separator in place I get good throttle response. The other muffler is drilled out and there is noticeable throttle bogging. I"ll also say before I built this exhaust I ran vintage VW tips in the 2-2 exhaust. Throttle response was ok but topped out at 7,000 rpms. With the non drilled 2-1 muffler I can hit 10,500 rpms easy when deciding to push it.
To me, all that means is you needed bigger main jets with the more free flowing exhaust.

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I doubt it's the plugs, but they're cheap and you may as well get new plugs or new caps or both. If you have the bike for any length of time you'll use them up at some point.
 

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Discussion Starter #18
Ok, I have non-resistor caps in the mail and am going to swap in a brand new set of coils I have laying around. If there is any heightened resistance in the ignition from age as well as running both resistor plugs and caps, that should take care of it. I am also going to switch from the wide perforated-style baffles in my exhaust to a narrower set of of louvered baffles which, hopefully, will add some back pressure. Everyone on the harley forums complains that the louvered baffles seem to be too restrictive of airflow for their bikes but it seems this smaller engine might like that compared to a fully open exhaust. If that doesnt work i will step up the secondary main.

In terms of sound, does anyone have any input on the difference between the perforated vs louvered baffles? I will be packing them with .5" thick ceramic fiber sheets. If not i guess i will find out ;)
 

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Discussion Starter #19
Just to clarify--- If I'm trying to modify the 6K+ RPM range, I would adjust the secondary mains, right?
 

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Jetting is more a function of throttle position than rpm. In neutral on the center stand you may be able to redline the revs and still be on the slow jet. Normal riding, at least in upper gears, 6000+ is probably most affected by the secondary main jet.
 
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