Engine Temp. Issues

[kx250ryder]

I recently overhauled my entire car (9.5 Pro), and I didn't think to check my fuel line lengths when I put new line on. So now, when I run the car there is a substantial difference in temperatures from beginning of a tank to the end 220 at start up to 270 at end (before the engine totally leans out). I have two theories on this:

1.) My jetting is off. I read somewhere that certain jetting conditions can cause the engine to get progressively hotter as the run goes on. But I can't remember which needle would cause this issue.

2.) My fuel pressure line is too short/long. I have inquired about this before, and couldn't get a straight answer about this. I figured that by shortening the line, this would allow the engine to pressurize the tank easier as the fuel level gets lower.

Any suggestions? Its kinda frustrating when my engine is lugging so bad that the car hardly leaves the ground over a jump at the beginning of a tank, yet is going like 25 feet off of the same jump towards the end of a tank, and almost blowing up from being too lean. Or is this common? I guess I should ask if everyone else has to adjust their carb during the SAME tank of fuel.

 

[CorradoPsi]

check for air leaks. retune from stock settings, and lengthen your pressure line to about 8-10 inches. make sure that your tank isnt cracked, that will cause a significant temp change once the level drops below where the crack is.

 

[olds97_lss]

Check what corradoPsi suggested. Sounds like a air leak somwhere. Or it's a savage tank on your 9.5...

I run a HB buggy and my temps don't fluctuate from full to empty. It runs about 210 once I tune it for the weather outside. That normally takes 1/8 to 1/4 turn on the HSN. I'm running an OS 21 RG. After getting the smoke coming out where I want it and the temps in the 210-240 range, I don't mess with it normally again for that weekend which consists of anywhere from a 1 quart to 1.5 quarts of running.

Same for my savage, but I have a buggy tank on it. It also has the OS 21 RG.

 

[kx250ryder]

How does one check for air leaks? I figure checking the tank and fuel lines would be easy, because filling them with water, and seeing if any leaks out would do the trick. But how do I test my carb or engine for such leaks? By the way Olds, I have an RG too, I love the engine. I don't think anyone else comes close on the cost/power ratio.

 

[olds97_lss]

Actually, to test for air leaks in the hose/tank, take the tank off the buggy, pinch the end of the fuel line shut, submerge the tank in water completely, then blow into the pressure line. If you get air bubbles, find them and replace what leaks.

The engine is hard to test for, but it's easy to just seal it up to avoid air leaks.

Pull the engine off the buggy, take off the back plate and the carb. Clean the neck of the carb with DA (alcohol), clean the joint where the backplate meets the crank case with DA. Make sure to clean both the backplate side and the crank case side of the joint.

Then get some sensor safe high temp RTV silicone sealant and put a small bead of sealant around the base of the carb, put the carb back on, press it down with your thumb so it seats good and tight, then tighten the carb neck bolt. For the backplate/crank case, put a film of sealant on the backplate where it will be contacting the crank case. Also put a film of sealant on the crank case where it will be contacting the backplate. Put the backplate back on and tighten all bolts.

This process seals the engine.

Also, check your header gasket where the header mounts onto the engine. If the gasket is shot (torn, burnt...) replace it with a new one. A bad seal at the header will cause the engine to run lean do to the pressure loss.

The RG is a dependable long lasting engine and not a bad price. But there are a few in the same price bracket that kick it's azz power wise. The mach 26, XTM 24.7, SH 28 just to name a few.

I choose the OS 21 RG because it's a lower HP engine (1.9hp) to help save the diffs and whatnot on my savage. It's enough power for what I do and they are really dependable.

You can get the sealant at just about any auto parts store.

 

[Plaidfish]

KX, when you shorten the pressure line you are more prone to fluctuations...the longer lines smooooth out th epressure.....I like the RG too....I use em for beating on my buggy now.....try polishing the crank journal and the fuel inlet on it and it really raises the RPMs....Iwas killing conrods on the last 2 I had until I dropped to 25% though....I don't think those conrods were meant to hold much more stress than they do now....

 

[kx250ryder]

Thanks guys, I will seal the engine, check the tank and lines, and try adding a bit to my pressure line this weekend. I will let you know next week how it worked out.

 

[olds97_lss]

crank journal and the fuel inlet

Not to sound like a complete douche, but what are these? The fuel inlet port on the side of the sleeve? I'm not sure what the journal is...

I only run 20% and have never broken a con rod. My one RG has 13 gallons through it. I had it pinched at 11 gallons. The only things I've needed to replace are the starter shaft and one ways. Oh, and a broken crank once... not really sure why it broke though (around gallon 4).

 

[Plaidfish]

the fuel inlet on the crank...if you look down the carb and turn the crank over you see the big opening the fuel goes into....the edges on those are a little rough on the RG...you can just polish the edges or get a little daring and bevel the edges to match the crank case bevel...don't worry about messing that up it's not like the sleeve ports that control timing....the crank being polished there just allows more fuel (or just smoother delivery) for the higher RPMs...the journal is th elittle post the conrod conects to on the crankshaft......that being polished just lets it move more freely it's more like having a bearing there instead of just a bushing.....I'm still looking for a better conrod to fit the RG cause that's the only weak spot I'm finding on that mill really....I'm afraid to try port timing mods on it until I find a stronger conrod......those parts are real easy to mod and don't run any real risk of F'ing it up unless you just go buck wild and try to grind it down instead of just polish it....

 

[niggle]

...don't worry about messing that up it's not like the sleeve ports that control timing....

Strictly speaking, this port does in fact control inlet timing. The crankshaft cut-out functions as a simple rotary valve.

I won't bore you with the technical details (unless someone asks) 'cos Eric will bust my a$$ if I do :hammer:, but suffice to say that if you hack about the crankshaft port and enlarge it significantly then there is a danger that your compression may well suffer!

As previously advised, careful bevelling and polishing here should do no harm.

 

[Plaidfish]

I opened one up pretty far on an RG and didn't see any real difference except it got more fuel and was revving much higher w/o getting leaned out....I guess that is timed....brain fart....but I dremeled the hell out of it before I noticed any difference....basically brought the bevel back behind the crank case on both sides when that port centers......still beveled it so it caught fuel smoother....what I should have said was it is not as critical as the sleeve ports.....at least in my experiments....

trust me I've hacked quite a few good mills into nice paperweights

 

[niggle]

I opened one up pretty far on an RG and didn't see any real difference except it got more fuel and was revving much higher w/o getting leaned out....I guess that is timed....brain fart....but I dremeled the hell out of it before I noticed any difference....

Yeah, that figures. Modest 3-ports like the HPI 25BB (and I guess the good 'ole RG falls into this category too) are quite conservatively tuned and you can see noticeable mid-top end gains by extending the inlet port timing on these engines.

The more expensive screaming 7/8 ports are pretty much on the limit as far as inlet ports go and there is a good chance that you'll spoil it if you start messing with the timing.

 

[Plaidfish]

yeah I've seen some of the local guys here get real crazy w/ timing so they basically run it sloppy rich and no brakes so the buggy winds out instead of loading up.....then run laps like that and hit every turn dead nuts.....one guy modded a Crono (?) and it was unbeleivable until one of the pro hot shots shows up w/ a 421 that was (hottinger) modded and that thing was crazy...I saw the esleeve out of it and it was sOOOOO freakin precise it looked like it was laser cut....I mean NO FLAWS.....I'd be scared as hell to try that...unless I had a pile of $500 mills laying around.....