Heat Seize at High Speed? CHT Sensor Leak?

[dresearch]

So to start off, I recently did an AF18E ZX swap into a Tact (Aero 50), all components are stock aside from a DD50 intake manifold (w/vacuum port to use with the fuel petcock under the seat), typical transmission parts, Daytona Racing CDI, 8-rated plug, and a CHT sensor/gauge setup. It's winter here and I did a late night run last night. The engine was running well, cruising around 40mph, when the engine starting bogging down. It was still pushing but slowly lost power until coming to a halt on the side of the road. Before it happened, I wasn't constantly holding the throttle wide-open, I started to hold the throttle wide-open when I felt slight power loss and couldn't keep up with traffic, then it slowly died after.

The engine would still idle once stopping on the side of the road, but when I gave it any throttle, the engine would bog and almost stall. Once I let off, the engine would return to idle again. I waited a minute and then tried throttling again, then it started revving up like normal and everything was fine after that... I rode off like nothing ever happened.

I took the panels off when I got home and found that the exit port from the cylinder heat shroud was wet from blowby, the oil was sticky, not wet like a bad leak. I took the shroud off and the fins near the back of the cylinder (near the exit port of the shroud) were a little wet. I couldn't identify any other wet areas on the motor or carb.

A couple of things:
- The head bolts seemed pretty loose... Not handle-turnable loose, but it didn't take much force to unbolt the bolts. I looked at the manual and it said 7 ft/lbs which seems really weak. I pulled the head off and the piston top and head where clean/slightly-dry, no signs of detonation (pic attached below). I looked at the metal gasket, and it didn't really look like it was leaking from any specific area, but I changed it anyway just in case. Is it bad to torque the cylinder head bolts past 7 ft/lbs? I torqued it to 9 ft/lbs.

- I'm running a CHT sensor ring on the spark plug. The crush washer that comes with the plug was removed before installing. When I pulled the plug out there was a small amount of oil sitting on the top of the cylinder (very similar to the pic attached, photo was taken from one of Cmoped9's previous threads on here). The threads on the plug were wet from oil too. The plug itself seemed nicely browned, gauging from the plug-chop chart (pic attached, sorry for crappy focus).

Could it be that the engine lost compression at higher temperatures/rpms because of a small leak from the CHT sensor washer? And once the engine cooled down, the sensor resealed itself? It ran totally fine after which confuses me. Engine temps didn't exceed 275F so it didn't overheat either (maybe a faulty sensor?). IÔÇÖve never been able to get engine temps past 275F.

- The Daytona CDI IÔÇÖm running called for a plug 2-steps higher than stock during ÔÇ£racing-scenariosÔÇØ. Is running a 8-rated plug too cold for normal riding conditions? In addition, IÔÇÖm also using the original Tact spark plug cap and boot. Could this potentially be an ignition problem? I havenÔÇÖt had issues riding with this setup for the past 2-weeks.

- It also can't be a fuel issue since the engine idled after bogging and drove off once the motor was fine.

I've exhausted all of the potential scenarios I could think of... Based on the photos I posted, does it seem like the setup is running a little lean? It confuses me because my engine temps seem to be low which points towards being too rich up top, but at the same time the piston and plug don't seem to indicate running rich. Could all of this be caused basically by the CHT sensor leaking under high temp?

Let me know what you think.

[dresearch]

head gasket leak. and looks like small cht leak too

Hopefully the new head gasket will seal it properly. Any suggestion on torque specs for the stock cylinder? I'm more concerned that 7ft/lbs is too weak.

[Rip_City_Spree]

Take it from someone who has broken a bolt off in the head. Beware of over tightening it's not very much getting that broken bolt out. I now tighten to close to 7lbs run it for a few miles and retighten. Then just check occasionally.

[Meatball]

Read the Torque Value for cylinder head here in the Service Manual around page 1-8, 1-9.

It does say 7 ft-lb is correct but there is a remark to the right...."apply oil to the threads and flange surface"
Im sure some of you do this always anyways bit I don't. I shove them in dry since Ive never actually seen that remark before.

I wouldn't crank down tighter than 7lbs, man.

http://www.hondaspree.net/other/Elite_S ... Manual.pdf

Side note: The Spree manual lists cylinder head torque spec with a range of 6-9 ft-lbs. Strange how they give you a torque range instead of a definite number like the Dio spec.

[dresearch]

that plug is WAY too lean.

Use permatex copper spray on both sides of the head gasket. Id do the piston and rings/hone.

The plug looked okay to me. Wouldn't the engine be running way hotter if it was leaned out? I can't get the engine hotter than 275F. Unless the CHT sensor is faulty..

[1man8scoots]

Once you go aftermarket oem specs are out the window.
You always read the manual for the kit and follow the kits specs. Not factory specs.

[Meatball]

I went into a small privately owned convenience store ran by a small Asian man that resembled Egg Chan from "Big Trouble In Little China". I purchased a Snickers bar that apparently had been sitting on the shelf for many years. The chocolate was sort-of a tan color, very dry and chalky. I didn't eat it and tossed it after the first disgusting bite.

Point: The color of that rotten chocolate is how you want your plug to look. Seek out Egg Chan and his petrified Snickers and you will find peace and harmony within your combustion chamber. That's what Jack Burton did!

[dresearch]

I went into a small privately owned convenience store ran by a small Asian man that resembled Egg Chan from "Big Trouble In Little China". I purchased a Snickers bar that apparently had been sitting on the shelf for many years. The chocolate was sort-of a tan color, very dry and chalky. I didn't eat it and tossed it after the first disgusting bite.

Point: The color of that rotten chocolate is how you want your plug to look. Seek out Egg Chan and his petrified Snickers and you will find peace and harmony within your combustion chamber. That's what Jack Burton did!

Hahaha, yeah I've got rotten chocolate on my plug.

I ordered copper gasket sealer spray, going to see how that goes soon.

Thanks for everyone's help.

[dresearch]

Once you go aftermarket oem specs are out the window.
You always read the manual for the kit and follow the kits specs. Not factory specs.

I'm still running the factory cylinder; BBK in the distant future. Just enjoying the speed I gained swapping from an AF05E.

[Meatball]

its lean. look at the piston. that bike is seeing too much heat.

Yeah, that piston looks too clean. There should be at least SOME carbon build-up. Normal conditions create carbon, its just the nature of the beast.

[dresearch]

Jet kit is coming in the mail tomorrow along with the copper gasket spray. Thanks again guys.

[dresearch]

A few updates since my last post...

I reinstalled the head gasket using the copper spray and the engine feels a lot more stronger throughout the entire power band. I also upjetted to a 78 main from the stock 75.

A few days later, I decided to upjet the pilot jet also as I was never able to fully tune the airscrew on the carb to the standard 1.5 turns out as stated in the manual. Please correct me if I'm wrong, but when I'm tuning the carb (engine fully warmed up after riding around the block), I'm trying to find the highest idle speed with the air screw. Currently, with a 45 pilot jet (standard is 38), when starting with the air screw turned 1.5 turns out, the engine continues to rev higher when the air screw is turned clockwise. Once the idle speed gets too high, I turned down the idle screw to lower the idle back down, then continued to turn the air screw clockwise. The problem I'm still having is the the idle speed continues to rise even with the air screw turned clockwise until the screw is fully backed into the carb. If I'm following things correctly, it sounds like I still don't have a big enough pilot jet in the carb? I'm not sure how much bigger of a pilot jet I would need to go to reach peak idle speed without the air-screw being fully backed in to the carb. I currently have the air screw turned 1-turn counter-clockwise out from fully shut since I didn't want to run the carb with the air screw fully closed. The idle screw is turned out in a safe range with room for adjustment. Throttle response is fine, no bogging throughout the entire range.

The tip of the exhaust is still completely dry, and the engine doesn't blow out any smoke clouds or anything close during warm up and initial running to signify that it's running rich.

Do I have another leak somewhere (I don't see any visual leaks or wet spots on the block)? Is it normal to be running a larger pilot jet on a basically stock AF18E block, using an AF25 airbox with the snorkel removed, transmission upgrades and an aftermarket CDI? I'm also running an 8-temp plug as recommended by the CDI manual. Idle is consistent after warming up. Winter temps in my area are 30-55F with humidity in the 70% range.

In addition, engine temps are in the 250-300F range cruising 3/4 to full-throttle, with peak temps around 320 when holding the throttle open for long periods of time (can definitely climb higher, but I let off once I reach around 320).

Let me know if you have any ideas.

[bonesv]

Sounds like you have it nailed. I would check the compression on the cylinder just to be sure it is in range of good health. Also, what type/brand of oil and which grade of fuel are you using?

[dresearch]

Sounds like you have it nailed. I would check the compression on the cylinder just to be sure it is in range of good health. Also, what type/brand of oil and which grade of fuel are you using?

Using Honda 2-stroke scooter oil on regular pump gas.

I still feel like it's running lean at low/mid-range since the pilot jet is maxed out, even for its size. I'm thinking there's still a leak somewhere, but not sure. It confuses me that I'm running a quite large pilot jet on a more stock setup.

[bonesv]

Re read the post and a 45 pilot is huge on stock pb carburetor, unless....there is no air filter in the air box. Or it is not oiled properly. Did you positively cap off the pulse-port under the oil pump area? If it's leaking there then you have symptoms like you described earlier.
I would do a 6-7 psi crankcase pressure test for leaks. Only test to 6-7 psi and monitor the gauge. Use a 0-30 psi gauge if you can get a gauge that small. 0-100 or higher is not going to be near as accurate. Just 6-7 psi watch for leaks in the area I mentioned and use soapy water in a spray bottle. Remove carburetor, air box, exhaust pipe and spark plug and seal off those openings first. Resolve any leaks and re test compression before riding. The 38 pilot is sufficient to use and if everything else is bone stock, the 80 main jet is plenty big or the 78 and raise the needle one notch. BR8 plug is what I use also.