breaking up at 70

mexipike · Full Member Joined: Jul 16, 2008 Posts: 49

I rebuilt my engine, with a little help from a mechanic, and have been really enjoying it. However, if you get over 70 or 75 or so (i don't have a spedometer, but was out with a friend who had one) and are trying to give it more to go faster it starts popping in the exhaust and bogs down. it didn't used to do this before. Is this a jetting issue, I'm thinking of going up a little on my main (i'm running mikuni 34 vms) or is it something else.

Thanks,

John

xsjohn · Posted: June 19, 2009, 8:09 am Post subject: Re: breaking up at 70

80 Special............you have a lot of carb work to do before you should try 70 for any more than a run up and back down............first of all the gearing is way to low for 70 for any given time and the carbs will need expert attention.......no way around that ....and just playing with the main jets will not be the answer.....and if you really knew how hot that thing was getting in the summer at those speeds you would cringe....I am...

xsjohn

IAmGrowler · Posted: June 19, 2009, 9:06 am Post subject: Re: breaking up at 70

xsjohn wrote:

80 Special............you have a lot of carb work to do before you should try 70 for any more than a run up and back down............first of all the gearing is way to low for 70 for any given time and the carbs will need expert attention.......no way around that ....and just playing with the main jets will not be the answer.....and if you really knew how hot that thing was getting in the summer at those speeds you would cringe....I am...

xsjohn

I know what you mean.

A '79 Special with no noticeable oil leaks when I bought it -- Leaked like a sieve (lower oil sump, now fixed) the day after I jacked it up to 70mph on an 80 degree day.

Any thoughts on oil coolers, John?

xsjohn · Posted: June 19, 2009, 9:28 am Post subject: Re: breaking up at 70

I just use the top end cooler..........but no cooler I have found will dissipate the heat fast enough that is generated above 80 degrees ..........the compression is just a bit to high for the cylinders and engine to kick off the heat............so I went to 8-1 ......not the American way to do with a bit less but I found it makes mine ridable anywhere any time without the typical XS hassles including noises and loss of power when it gets hot......so actually at the end of the day I lost no performance.....in my mind I gained some.....but who would listen to an ole fart anyway........it's all the more more more thing......and in my minds eye hopping these up would be totally bassackwards to progress on the above matter......... heat is not your friend........don't fly too close to the sun and all that good advise........I must be just getting old........

xsjohn

mexipike · Full Member Joined: Jul 16, 2008 Posts: 49

Yeah the summer heat is definitely rough. I'm in Texas and it's around 100 everyday this time of year. Unfortunately, I got to be on the highway for a good while everyday. Can I make this thing cruise at 70 or should I just give up.

xsjohn · Posted: June 19, 2009, 10:33 am Post subject: Re: breaking up at 70

You can surely make it better........I did..........Just depends on whether you want to go through a bit of a mechanic thing.........and 65 will end up being a better sustainable speed even with 18/30 gearing and the carbs fixed right and the timing set to better suit that......at least that's the way I see it.......after 10 years of studying this topic on the XS ....and 40 years of dicking with these things...........

And until you get the plugs burning with 1/3 black up the side of the electrode and some grey color on the electrode at sustained highway speeds the heat will just continue to rise..........for those that are interested here is the latest 8-1 CR with Autrolite 64's....and the correct R/L custom needles ....46 pilots and 132.5 main jet.....55 to the gallon too.....no engine noises and much cooler...... Very Happy

xsjohn

mexipike · Full Member Joined: Jul 16, 2008 Posts: 49

So I took the carbs apart a little bit today. I realized the slide on the right side was a little lower than on the left. I got them all straightened out. I also moved the clip on needle up 1 notch, so now it's at the second notch from the top. It actually is performing notably better now, however it still breaks pretty much at the top of every gear at hard acceleration. Still working at it.

nudude53 · Posted: June 20, 2009, 12:58 am Post subject: Re: breaking up at 70

John;
Those plugs look real good, but who does your nails?

xsjohn · Posted: June 20, 2009, 7:47 am Post subject: Re: breaking up at 70

Glad I didn't lay them on my leg.......... Laughing

xsjohn

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