300 falling on its face

[MarkinAR]

So here's one I haven't beat yet, could use some input. Honda 300FW was running fine when one day it started bogging at WOT. Figured dirty carb so I cleaned it and still the same. Cleaned again once more by soaking overnight in thinner and then compressed air. Back together tonight and still falling at WOT. Tried a known good plug...nothing makes sense here. The float bowl does seap a bit due to old gasket, could it draw vacuum enough to interrupt fuel? 

[Frank Angerano]

Absolutely will draw air intake on the bowl with a bad bowl gasket.  What happens is you get a corrugation of fuel and air going up into the needle.  Its like a carbonated effect. 
I would shut the fuel off and run the engine dry. Unscrew the bowl drain screw on the bottom of the carburetor to get all the fuel out. Wipe down the edge of the bowl where it meets the carburetor and run a beed of silicone around the seem.   Let it dry good over night and reset everything back as it was and fire it up.  If it runs good then you need to put a new rubber gasket on the carb. 

[MarkinAR]

Was considering running a bit of silicone to test before I ordered a rebuild kit just for the bowl gasket. Thanks for confirming a hunch. The gasket is all there, it's just flat from years of use. Probably the original 98. 

[MarkinAR]

Think it may have been the bowl gasket. I drew a bead of ultra gray and let it dry. Put it together and it seems to be back to normal. I also made a pump block off out of thin steel. The diaphragm looked a but rough and we never need the manual pump so it's just blocked off now. I left the pump so I could reuse the original screws but it's just decorative. 

[Frank Angerano]

Very nice work! I love making sh** work! Nothing better then taking some leftover stuff you have laying around and using it. 
👍🏻

[MarkinAR]

Same. Its actually left over metal from when I made a battery tray for the Kodiak we used to have. wife was busting my chops about scraps of wood and metal just last weekend! Here is what it looks like now with 28's and 420 Rancher shocks. 

[Frank Angerano]

Looks like a beast.  
Dam those 28's are big! Any clearance issues over rocks and bumps ?

[MarkinAR]

Gobs of clearance but too much tire. It needs gear reduction to turn them in peanut butter. Just have to go slow and not burn the clutches out. 

[Frank Angerano]

Lol I bet. I was wondering about clearance and never even thought about the gear ratio.  

[MarkinAR]

Well that wasn't it. Have tried moving fuel clip, cleaned carb and its spotless. Tried another CDI and regulator. It just acts like a rev limiter at 60%  and it did not do this before rings and valve stem seals. Stumped. 

[Frank Angerano]

Hows the plug look? 
Timing spot on ? 
Valves adjusted good ? 
Throw an inline spark tester and see if spark is breaking down at 60% throttle.  

[MarkinAR]

Plug looks good. Guess I'm going to pop the rocker cover off and double check timing. Fire and TDC are like 1/4 from each other. Perhaps I have it timed to fire and not TDC. Runs like a champ otherwise.  

[Frank Angerano]

Could be a simple timing thing.  

[MarkinAR]

Guess I've largely discounted timing bc it fired right up after rebuild and runs perfect otherwise. Maybe with increased RPM a slight mistime becomes a won't run situation. 

[Frank Angerano]

It could be. I have seen instances where timing was set bit once tightened on the chain tensioner it throws it off.  
its a long shot but im just throwing things out there. 

[MarkinAR]

Well I'll be. Turns out I had it timed to F instead of T. Bumped it 2 teeth and it runs like a scalded dog. Amazing it ran so well 2 teeth off before. 

[Frank Angerano]

Haha yea boy! Way to go brother. Love easy fixes! 

[Finnforest]

Seems you have the same tire size front and back, on my Honda (300 trx) i have different sizes front and back, have you changed the gear ratio somehow? I want big fat tires on mine aswell but i think rip the 4wd apart if the ratio is not correct.

[MarkinAR]

@Finnforest It's fine to run the same size tires front and back.  If you were to run it on pavement for miles the ratio difference would become an issue over time, but for a 300 that will never be fast or used for long distance highway travel, it's fine.