Seeking VTR250 Interceptor info - Sportbike Forum: Sportbike Motorcycle Forums
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post #1 of 3 (permalink) Old 02-14-2007, 03:18 PM Thread Starter
Join Date: Feb 2007
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Seeking VTR250 Interceptor info

Hi all! Came across your great site here while searching the web for VTR250 info. From the posts I have read, it seems Lord Duckhunter is the VTR master!

My 1988 model is still pretty much stock, about all I've done is install the Dynojet stage II jet kit and a Yoshimura slip on with the baffle removed. Also cut the old paper filter out of the filter plate and dropped in a K&N flat panel air filter from a civic. She runs a lot better than stock, but I recently acquired a 1990 model as a project bike and want to go a bit further on it.

Had a few questions for anybody who has upgraded their VTR, I'm hoping your experience can save me some time and cash. The bike came with the VTR specific Supertrapp muffler, so I do have some adjustability on the exhaust side of things.

First, which is the better jet kit, the Factory Pro or the Dynojet? I'm pretty happy with the Dynojet, but have zero experience with any of Factory's products. I plan on adding the K&N air filter to this one as well.

I'm planning on putting in the Progressive Suspension fork springs but I have heard mixed reviews on these. Greatest mod ever or a waste of money? I am a little heavier than the average rider if that figures into your advice. Also, the Race Tech cartridge emulaters are available for the VTR forks, is this a worthwhile mod?

Internal engine mods is where I am a total newbie. I have a mill and lathe so simple machining like slotting cam sprockets and such would be easy, but extensive specialized mods like lightening the crank is out. With that in mind:

The Japanese domestic models with this engine crank out 43HP according to the literature. So far the only two major internal differences I can see comparing specs is the cams are of a different grind, and the ignition timing is advanced something like 5 degrees. Is this correct?

Are the Japanese spec heads different other than the cams? I have seen some claims that the valves were 1mm larger and that the internal passages on the intake side varied somewhat between models. I can purchase cams fairly affordably but was wondering if the head should be swapped out as well for maximum effect. Is there a better alternative to the Japanese cams? Slotting the stock cam sprockets and adjusting stock cam timing? Looking for streetable horsepower here, not an all out race bike.

I plan on slotting my starter clutch cover to advance the timing, what is the general range I should set it to for maximum power using premium (93-94 octane) gas, stock compression and possibly Japanese spec cams?

Any other mods that would be worthwhile and inexpensive?
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post #2 of 3 (permalink) Old 02-20-2007, 11:03 AM
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Join Date: Jul 2000
Location: Memphis
Posts: 458
You are talking about a 250cc bike here... No matter what you are doing to it, it will remain "streetable"

My best advice is to just do the jetting & airbox mods & then go after the proper spring rates to get sag etc. Utlizing high dollar suspension components or even grafting other front ends onto the bike etc just becomes a point of diminishing returns for anything other than the novelty of impressing others with your determination.

Spending a lot of money on this bike is just silly. Trust me we turbocharged one back in the early 90's Spent $3500 for a Mitsubishi Turbo unit for a $1200 bike & with the blow thru carbs never did get it to run quite right as it truly lacked consistency.

More importantly when you start doing internal engine mods on these things the reliability goes to shit. You just can't keep them together afterwards.

VTR250 collectors generally are a cult breed & know the limitations of what they have. They are chasing a small lightweight nimble package & a bit of rarity. If you really want a faster bike then just go buy one & you'll suffer a lot less aggravation in the long run.

If you just want something new to experiment with then try lightening the flywheel and see how that improves the spin-up
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post #3 of 3 (permalink) Old 02-21-2007, 05:08 PM Thread Starter
Join Date: Feb 2007
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Actually, spending as little as possible is my goal. I have about $100 in the bike and figure if I can keep the major expenses down I will have around $600 or less in it when I am done. I can hardly purchase another bike for that, besides I have always preferred the handling of the VTR to bigger bikes anyway. Bought my 88 back in 88 and have never found anything I like better.

The Japanese domestic models of these bikes cranked out 43 HP stock and are still going strong at this late date, so reliability seems to be there even with the extra HP if you use factory parts. I can import a set of JDM heads with cams from NZ for around $150US plus shipping, shipping being more than the heads! Main reason I asked about the valve sizes and internal passages. Shipping 4 cams is a heck of a lot cheaper if the heads themselves are identical.

So which jet kit is better? Factory or Dynojet?
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