I have an 04 ds650 baja x with the following mods and need advice on what octane fuel i should be running. It has a big bore kit with 15 to 1 compression, polished head, and FMF titanium 4 exhaust. It has the original carb with needle and jet mods done. Normal operation elevation is about 4800 ft. This is a trail quad. Not for racing. Need to know what fuel would work best for me.

 

First off, welcome to the forums. Now, by big bore are you talking about a 720, 730, or any of the bigger bores that are out there for the DS? Most folks step up the carb when they go big bore, not sure why yours didn't come with a TM45 or 48, of a Lectron 46 or 48. The stock carb should have atleast had the OMR stock carb mods as it is good up to around 65HP. But big bore needs more air and more fuel than what the stock 43mm can normally deliver.

I would at a minimum run 100LL AV gas. There is a lot of discussion lately about E85 but it gets technical. It's 105 octane but gets consumed quicker than most pump gases.
Again, welcome aboard.

 

If your really 15:1 comp your going to need a lot more than 100LL...

You said a trail quad. Are you sure its not 11.5:1?? 15:1 is some serious compression for a trail bike.

Who sold you the BB kit? WHat octane do they recommend?

 

Im guessing a typo ... 15:1 is not gunna happen...

11.5 is my guess ....

87 pump gas .....

 

not a typo. comp. is 15 to 1. my son who is partners with me on it ordered the piston and thats what we ended up with. I know its a bit extreme for trail but thats what i have. it wasnt a big bore kit. I had the jug bored and replated instead of sleeving it. what i have been running is two parts 110 race gas and one part 91 pump gas. just wanted some more input on whether or not that was about right.

 

Ok what formula did you use to come up with 15:1 that is super extreme unless you are using a formula that I have never used t acheve this. What is your bore? Stroke? And cc of the head?

 

I guess that was to much information to ask for.

 

nobody makes a 15:1 piston that I'm aware of. 14:1 is about it . there is no need for a 15:1 trail piston...

 

sorry just going by what the paperwork that came with the piston said. it is a JE piston and it SAID 15 t01. 13 to 1 was what i wanted but this is what my son ordered. wasnt looking for a debate here. just wanted a little input.

 

you need a debate, the is no such thing as a je 15:1 piston ...