I was shooting the breeze after a race with a guy this last weekend, and talking to him about my hot start problem...
Without discussing my actual bike, he said that most 4 stroke's hot start problems, derive from the de-compression mechanism.
I took 2 hours of adjusting the fuel setting while the bike was on a dyno, and only paid attention to the AFR. I got it as close to 13:1 as I could across the board, but the bike still acted up once it was good and hot. I originally thought my problems were from being too rich off the bottom rpm range, but now I'm beginning to 2nd guess myself.. WHen you guys stall out in a race does your bike fire right up? or does it take several seconds to a minute of embarassment before it fires again?
Hot start causes
I had this same issue with my X440S. Plug looked perfect, bike ran great - started fine when cold - but was killin' me on the hot starts. Turns out your "second guessing" is probably right. After way to many months of testing with injector offset and injector flow settings (I was always getting the advice to lower injector offset - not the fix for this). The final resolve was to raise the Throttle Offset by .5-1.0 as the hot start issue was actually being caused by a lean condition. The Throttle Offset compensates for air leaking past the throttle body plate.
when I slapped the bike on the dyno.
1st run showed it was WAY lean on the bottom, and Rich on top.
I ended up with an offset of 1.4 and a flow rate of 2500
Which gives lots of gas on the bottowm, and take a little off the top... It did however start acting up the last few runs, but not nearly as bad as during the last few races.
Now I calculate a need for fuel below 4500 rpm, and a need for fuel above about 7000rpm
But They guys at the shop say I'll never get the AFR line to flatten out.
Here's the AFR readings off the dyno on my final run...
1st run showed it was WAY lean on the bottom, and Rich on top.
I ended up with an offset of 1.4 and a flow rate of 2500
Which gives lots of gas on the bottowm, and take a little off the top... It did however start acting up the last few runs, but not nearly as bad as during the last few races.
Now I calculate a need for fuel below 4500 rpm, and a need for fuel above about 7000rpm
But They guys at the shop say I'll never get the AFR line to flatten out.
Here's the AFR readings off the dyno on my final run...
Did you change the Throttle offset too or just the Injector offset? I'd like to see an AFR post with the Throttle offset tweaked to see it's actual effects on the start up/lower RPM fuel mixture. I have never run my bike on a dyno to check the AFR - I only get to do the "Real World" testing (unfortunately). That of course means I'm 15-20 miles from camp and at that point find out the hot start issue would still be there. I've run lower and higher than stock settings on the injector offset with my preference being just slightly higher than stock. No amount of tweaking the injector offset or injector flow fixed my hot start - just an increase in the throttle offset.
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CannondaleRider
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- Joined: Wed Mar 10, 2021 10:41 pm
NO throttle offset, I think m,y throttle % is closer to 6 than 4 ...
I found I was way too lean off the bottom, so it seemed like my hot start problem was caused by this.
I've found that twisting the throttle a hair while cranking usually gets the bike started...
I still contend the only good way to resolve this is to build a unique and custom map for each bike, The shop confirmed that on other bike you could install a perfect map off one bike, and it would run like poop on another bike, even with the same configuration as far as pipes and mmods.
I found I was way too lean off the bottom, so it seemed like my hot start problem was caused by this.
I've found that twisting the throttle a hair while cranking usually gets the bike started...
I still contend the only good way to resolve this is to build a unique and custom map for each bike, The shop confirmed that on other bike you could install a perfect map off one bike, and it would run like poop on another bike, even with the same configuration as far as pipes and mmods.
Hey zero , next time you try a hot start. Tap the starter button twice wait 2 seconds and then crank. I have a quad with a similar problem. It seems doing a quick cold start routine makes it start much faster . If I try to crank start it right away I always have to crank it for about 5 seconds straight before it will fire. This procedure takes as much time but seems to work better. Must be hot starting way to lean. Runs great though.
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cannondale27
- Posts: 0
- Joined: Wed Mar 10, 2021 10:41 pm
****** has the key to the issues.3.5-4% throttle opening.What that means is to tune for stroker or what ever majority of tuning must be done within map rather than offset and flowrates.Adjusting the throttle offset does help in starting though.Goal of mine is maps made to compensate for mods while using factory settings.
I'll make sure I'm not past 4% throttle this weekend...
It's a big weekend, they are having KTM demo days on a 4000 acre ranch sat followed by hare scrambles Sunday. If I get embarrased by a big bad '06 ktm 525, I will be racing the KDX in the hare scramble. The atk does well, until I stall it out, then I get passed while I am on the side trying to get the thing to start...Liek I said before, I dumped a whole lot a gass into the bike on the bottom rpm range, so hopefully It's not has hard to start..
It's a big weekend, they are having KTM demo days on a 4000 acre ranch sat followed by hare scrambles Sunday. If I get embarrased by a big bad '06 ktm 525, I will be racing the KDX in the hare scramble. The atk does well, until I stall it out, then I get passed while I am on the side trying to get the thing to start...Liek I said before, I dumped a whole lot a gass into the bike on the bottom rpm range, so hopefully It's not has hard to start..