Jetting for new fuel

[The Honda Pilot]

After purchasing a 05 CR 250 I've came across a small issue. The past owner raced it in either the B or A class MX. The bike runs very well, but only on Renegade SX2 fuel which is leaded & oxygenated. I've tried VP C12, Sunoco 110 & various other leaded but NOT oxygenated race fuels. It runs like crap on 93 octane pump gas & leaded race fuel. I would continue to use Renegade SX2 if it wasn't $21.00 per gallon! :(

As I've slowly found more time to ride, so it's getting more expensive as time goes on. Mainly riding woods now so we will ride all day long and burn 3-4 gallons each time we go out.

With the pump gas & the leaded fuel it will run rough, smoke more then it should & spooge out the silencer all over the swingarm & plastics. With the SX2 it runs like a raped ape & does not smoke or spooge.

I want to jet the bike for 93 octane pump gas or atleast a cheaper blend of race gas. Where do I start? It seems to have the most issues from idle to mid throttle. So I was wondering if I should go one jet leaner on the pilot & move the clip one position leaner. I've read that oxygenated race fuel generally makes the engine run richer. But in this case it's acting the complete opposite. From just off idle with pump gas it will sound like a studder or slight miss. The throttle seems more jumpy and not nearly as smoothe with the expensive fuel. What really annoys me is while riding at the lower speeds the bike loads up pretty bad and is really hard to get it to clean out. Every couple minutes I have to rev it to the moon to get all the excess fuel pushed out.

I am running amsoil dominator at 32:1

Only other mods that I can visualy see is V-force reeds & pro circuit pipe & silencer. I was wondering if the motor was built and that is why he was running the oxygenated fuel or if it was just used for maximum performance. The jug & head still look factory.

Where should I start?

 

[RM_guy]

You can try to jet it (check the thread at the top of this forum) but you will more than likely need to have the head modified to reduce the compression. Sounds like it was set up to run a high octane fuel and you risk detonation if you try to run pump gas in it.</SPAN>

 

[The Honda Pilot]

IM still curious as to why it only seems to run good on oxygenated race fuel. Is there any oxygenated fuels that are less then $20 per gallon? im guessing the answer is no...

 

[Rich Rohrich]

IM still curious as to why it only seems to run good on oxygenated race fuel.

If you think about what the term "oxygenated" means I think you can answer that question yourself.

 

[The Honda Pilot]

I guess I will continue to use to the fuel.

 

[The Honda Pilot]

Just another questions that may change things up.

When I picked up the bike the previous owner had 93 octane pump gas in it and Belray H1R oil in it. I changed it from that last tank on to Amsoil Dominator. Could a bike be specifically jetted for one perticular oil?

 

[Rich Rohrich]

It's not the oil. Regardless of the fuel you decide to use you need to learn how to jet. The bike will run like a champ on C12 if you learn how to jet. If you don't bother with jetting you'll spend the rest of your time with that bike chasing some half-assed fix to work around the fact that you didn't bother to learn how to jet. Did I mention you need to learn how to jet your bike for your fuel?

 

[RM_guy]

Here are some good jeting links

http://dirtrider.net/forums3/showthread.php?42618-Jetting-Links

 

[sbest]

Absolutely right you have to learn to jet, but you may have to undo some mechanical mods also if the bike was set up for race gas. Typically the compression is raised and the timing advanced to take advantage of the higher octane. Usually the head is "milled" to raise the compression and close up the quench. The easiest way to correct this is to hand cut a couple paper base gaskets for under the cylinder. 0.010"-0.020" will do the trick and not hugely affect port timing or quench. Then check that timing is stock.

I did this to get my street legal KTM to run on 83 octane regular (often all rural stations have) with very little loss of power. Unless you are racing, you don't need the last 5% of power and the 300% gas cost.

Steve