Hard Starting with Hi-Comp Piston- solutions?

[Spokes574]

I put a hi-comp piston in my Y09 CRF450R and the starting is atleast 3-4 kicks more than all my friends with a stock piston. What causes this and is there anything that I can do to improve? Such as make an adjustment to the map?

Thanks,
Spokes574
Pleasanton, CA

 

[mideastrider]

I would not think that Hicomp piston would affect starting in a negative way. Have you double checked timing and valve clearance. Sounds like something may be a little off somewhere. Don't really know how it effects an EFI bike though.(just noticed its an 09)

 

[bwood]

Just a note, most high comp pistons require high octane fuel (sometimes more than 93). Double check your timing and valves, make sure the auto decompressor is adjusted correctly and make sure there are no air leaks.

 

[Spokes574]

I did not think about the auto decompressor...
I have a modified one from MDK.
I will give them a call tomorrow and see what they say.
Thanks.

 

[cthowards]

I have a 2005 CRF450R with a high compression piston and I have found that it runs much better with race fuel (I run Sunoco GT360 Plus). As for starting, I just kick it really really hard each time and it starts in 3-4 kicks cold and 1-2 kicks once warmed up.

Good luck.

 

[Spokes574]

[Spokes572] I talked to my MDK tuner "Michael" and he does not think that the valves need adjustment yet (~12hrs since top end work) and says the decompression has no adjustment.
He asked me to bring it in next week to check the valves since he is very busy this wk.

I do not have the stock map since I have a Yoshi Pipe, porting, hi-comp piston, stiff clutch springs mated to a hydraulic clutch - MDK installed a different map. In total about 9.3hp over the stock engine on the top. So possibly the map could be the issue? I do not know but it takes about 21+ kicks to turn it on cold, and once warm it's a hit or miss. Sometimes it turns on on the 1st kick, other times/most it takes 8 kicks on avg. 8 to me is too much, especially when I see the stock bikes turning on in about 3 kicks. The plug gap is perfect. Kicking on this bike is top dead center and a smooth slow kick is what ussually works for me - or possibly this technique does not work?

Yes - Race gas (~25%) does improve the porformance with the new map, especially when I lug 3rd, the little bit of pigging I had is totally gone and the bike seems to pull harder and stronger in 3rd when I lug instead of down shifting to second.

I got to get this starting sorted out quickly. I wonder if I remove the backfire screen if that will improve starting? any thoughts? I do not want to remove in case it screws with the map settings. Is there a particular map setting or specific map parameter that should be adjusted to compensate for the hi-comp piston when first turning bike on?

Provide advice.

Spokes572
Pleasanton, CA

 

[greenteam403]

You need at least 95 octane for this app to run at its best. Give your bike a tip until a little gas leaks out before you start it. That way you know gas will be there first kick

 

[Spokes574]

I like the comment about tilting the bike to get gas into the carb - that worked great on my Y05, but on the Y09 their is no carb vent hose to ensure the carb has gas in it.
spokes574

 

[spark250]

wouldn't the mods, especially the changing of the map make it hard to start? I don't know a whole lot about the hondas but my yammie has what they call a neutral switch. From what I understand it retards the timing when the bike is in neutral to make starting easier. I would assume a new map would advance the timing and make it harder to start?
In my experience, not just limited to bikes, higher compression motors are harder to start!

 

[IndyMX]

I like the comment about tilting the bike to get gas into the carb - that worked great on my Y05, but on the Y09 their is no carb vent hose to ensure the carb has gas in it.
spokes574

What with it not having a carb and all.. Fuel injected bikes don't really benefit from the tilting the bike on its side trick.

 

[_JOE_]

What with it not having a carb and all...

I see it now.........some guy with his 450 on it's side jumping on it trying to gas to come out. :laugh:



Definately sounds like a mapping issue to me. Time to go back to the shop. Too bad you can't swap the pilot jet and keep riding huh? :nener:

 

[Spokes574]

STATUS:
I changes the oils, cleaned the filter, double check spark gap.
I did not get the valved checked but bike only has ~14hrs since port job.
Ran the bike this weekend and had no issues what so ever.
Bike turned on on 1-3 kick every time- even when cold it took 2 kicks instead of the ~21 kicks of the previous 2 weeks.
So I am confused as to why past several weeks difficult starting and
all of a sudden this week ran perfectly? I am running 1/3 race gas now.

Oils did not look too bad- only 3hrs. I did sniff the motor oil to see if there was any gas in it, I did not see any bubbles (CRF450R's Y09 trickles gas from carb and gets down into oil) some bikes have this real bad. I have never noticed an issue on my bike
so maybe had something to do with the oil mixed with a bit a gas? I do not know but I plan to change the oil every other ride for the next month and then go back to 5hr intervals and see if there is a degragation in starting. I just happy it went away without costing me money or a trick to the race shop.

I want to thank everyone for their ideas and support.

Spokes574