Trying to reduce heat in a DOHC...in a desert

[Castle Bravo]

Hello all,
I'm new to the forum but am presently collecting parts for my 1979 and will soon begin (and thoroughly catalogue for everyone) a hybrid genre, mostly cafe' build. I live in a brutal, merciless and scorching desert called Phoenix Arizona. Its already a given that 5-6 months a year, the bike will sit and cannot be taken into 110-118 degree weather. I recently read an ad for a company that sells carb alteration kits designed in part to help with heat issues. They are larger jets and the idea, as they espouse, is that running rich keeps a motor cool. They also say, specifically their kit improves the cooling of a motor that has low-pressure after market exhaust...which of course makes a motor run more lean. So it all comes down to, is that real? Will it run somewhat more cool rich? If I can drive in 100 degree weather rather than 98, I'd get 15-20 days a year back. Also, would header wrap prevent heat from drafting back onto the engine block or would the header wrap simply trap more heat against the exhaust ports, making the heat worse? If you have any other suggestions in regards to heat, please illuminate me. I want to use an oil cooler and will when I can but cannot presently invest in one. Thank you for your wisdom,

 

[amc49]

You NEED an oil cooler, period. The 750 (no cooler) will run hot when pressed and oil pressure drops until you ride easier to cool it back off. Here in Texas and up to 105 temps. Use either the 900 or even better 1100 cooler setup.

There is literally no difference in 98 and 100 other than two numbers. I rode in 100+ forever. We hardly get to 110+ though. '80 750F.

Richer DOES cool motor however it has to be balanced against the fact that hotter air is LESS DENSE meaning it has to be leaned to make up for that. One balances out the other. In other words stock jetting on a stock engine is as close as you will get until you make engine changes like header. Remove the idle limiters off the mixture screws and then screw the screws out a bit more (2 1/2 -3), that takes care of the lean idle.

Header wrap is a scam. It is supposed to hold heat in the exhaust but unless running a turbo you have already lost the heat from engine which is where it gets used. A hotter pipe makes your exhaust tuning calculations change but since they all get averaged anyway in the header design, why they are a farce. I can tell you they positively DO corrode exhaust faster if hot and it rains where you are, the water trapped in wrap then eats the exhaust alive. Wrap is a kid rider's gimmick, I sold it to them all the time at the part store.

The heat here will destroy the rubber cam chain tensioners pretty quick, they show myriad cracks in the rubber at 25K miles. Why many of the motors go down, the tensioners break eventually. The other biggie is the valves can't be set like you think, they give misleading numbers and why you set to .005" minimum rather than the Honda number of .003" which can burn valves pretty quick. The stock OEM cam clearances in head have them running looser than the valve setting itself and then turning cam around will get different valve clearance in different places around the cam base circle because the other valvesprings are shoving the cams around in the head clearance. meaning what you see is not what is there when running. A big problem and why so many of the bikes went on sale with crap running engines that then had rookies going after perceived 'carb problems'. Put carbs back to OEM and then set the valves right and then what ran like crap runs perfect, I bought and sold a couple like that myself. Easy money if they didn't drive it long enough to burn the valves. The valves on these close up more than open with wear. Don't question it just accept it.

Thicker oil. I used straight 40 and many use 20-50. Switch to 30 during the winter.