Modern Vespa

Took my '60 TV175 on the Moto Melee this last weekend and really got to know it better than I had in the last 17 years of owning it. It had soft-seized a year ago after fitting a new piston and exhaust so I went up a jet size and blamed the mikuni carb for leaning out at high RPM. It was boggy but I figured it would make it. I also fitted it with exhaust and cylinder head temp gauges so I could keep an eye on things.

Even running really rich the exhaust would get really hot at high RPM. I was perplexed but limped it through the 280 miles of the first day. Fifty miles into the second day I was forced to downjet to get over a 4000ft pass and could finally see what the temperature was doing with reasonable jetting. Much better power all around but still the exhaust temp would go ballistic if I tried to rev over 5000 RPM.

Finished the rest of the 740 miles with the leaner jetting and just kept my eye on the gauges. At this point I think the exhaust is too restrictive as the temperature change is huge and comes on really fast as you rev past 5000. Point is that without the gauges I'd still be chasing the jetting instead of turning my attention to the exhaust. Next steps will be to add a few holes to the exhaust and see how it changes.

head temp didn't rise proportionately with exhaust temp?

I would like to see how you hooked up the temp guages

I don't know how he did it, but you can buy EGT's and various other thermocouples and gauges that are somewhat universal.

EGT's typically require you cutting a hole in the exhaust manifold, welding a nut there, and then screwing in a thermocouple with an electric wire lead coming off of it, that runs to a gauge.

I believe "westex" is a company that a lot of scooter folk use, because their setups are small and unobtrusive.

It did but the head temp does not react as fast. In general the EGT goes up with RPM and the CHT drops with rising RPM (due to forced air cooling). In this case the EGT would go from about 600-650c to well over 800c very quickly.

I used a clamp on style EGT and the CHT fits under the sparkplug. I used some plastic pipe to create a mount for the gauge. I'm going to ditch the speedo and move the gauge there permanently.

Ha..trip out

You are really going to ditch your speedo? Could you just get a "cluster" of guages and mount them somewhere?

This is cool..

Hey for that clamp on egt, did you still have to drill into the pipe for the sender, or does it sense the temp from the outside?

I'm ditching the speedo on my series II, as well, but that's where the tach is gonna go.

I had to drill a 1/8 in. hole for the sender, puts the tip of it in the center of the exhaust flow.

I'm going to use a stock lens and mount the gauge from the back to keep the same smooth lines.

i'm wondering...if the spike is a result of the nature of the harmonics between combustion and backpressure. wonder if you lower your pressure behind the gauge, if it will exacerbate the spike.

You could use a RAM mount attached to your mirror stalk for the gauge,
I use a RAM mount attached to the mirror stalk for my Garmin GPS.

Oh...Wait a second, You have a legshield mirror, I'm not a fan of those,
They tend to bump into things and cause too much damage to the legshield.

Why can't they make them flexible and have them springy when they hit something?

Nevermind, That's too simple of a solution,
They'd lose too much business from not fixing legshields.

The lambretta is really lacking for a place to mount mirrors yet alone anything else. I hate the legshield mirrors as well but they are really the only option.

i am not interested in either of my speedos and have been wanting for something usefull.

a tach is in the works for the et3,but i think that is not as usefull as a proper temp set up.

thanx for the clue oops

I'm very interested in doing this after a soft seize last year (because of running out of fuel) and another at the beginning of this season after a rebuild (I believe the timing and/or jetting was off -- I've adjusted both).

I have a useless speedo (I have hooked up a cycling computer instead) and would love to put in some temp gauges.

How does the CHT lead fit under the sparkplug? Do you have to make any kind of modification to the head itself?

Thanks in advance!

fwiw, I have had good luck so far with the 'hidden' mirror mount Casa sells. It uses only one of the headset screws, so no drilling required. I've been running it for a year and it's been very stable.

Looks like this:

I did a short write up on my EGT/CHT setup. May be useful to some. I'm adding this setup to my MotoBi and as soon as I've got cash for more gauges I'll add it to the Maicoletta as well. This has worked well for me but your milage may vary.

http://oopsclunkthud.com/tuning/gauges.pdf

Nice writeup, Patrick. I'd like to see a bit more info on what's needed to run... how did you hook it up, what powers it, etc ?

I'll add to it as I setup the MotoBi. I'll list the part numbers, costs, and show pictures of the process. These gauges are self powered using the temp difference between the gauge and the sender.

Very nice.

Nice to see the CHT probe on your spark plug. I figured the clearance on the cowl was too tight and would require putting the probe on a cylinder stud.

I know this is an old thread..but what the heck!

Has anyone figured out a good way to mount a 2-inch round CHT?

I have one on the way and have already run a tracer from the cylinder to the headset.



Mine is a single 100 - 700 F

I also have a shell on the way



I figure I don't want to mount to the headset as it will pull the wires when turning.

Any ideas or suggestions appreciated!

Thanks for the write up. That and a conversation with a total gear head convinced me that it is the way to go!

Here's how I mounted it on my smallframe (with a P headset) I've also been playing with the idea of making a fitting to place it where the speedo goes.

I just looked into this thread and I have a product suggestion and a couple of questions:

I was looking for a similar more information speedo and found this some months back:

http://www.electrosport.com/street/speedometers.php?source=adwords&gclid=CITXt92p150CFUpK2godlCt6Sg

I would love to have the fuel gauge.

But here's the question...
If you don't have a battery how do you add one?

[quote="oopsclunkthud"]Here's how I mounted it on my smallframe (with a P headset) I've also been playing with the idea of making a fitting to place it where the speedo goes.

I really like that position. What did you mount it to?

Oh yeah this is going on a 67 GT (Sprint)

I used the screw mounted gauge holder and just drilled holes in the headset top, 3 sets of holes before I got it in a position that worked. Not sure I'd go that way with a sprint.

I'd look at making a bracket coming off the windscreen/mirror mounts on the headset. Figure out where you want the gauge, where you can bolt to, and then make a bracket to connect the two.

Thats what I was thinking. I'm just gonna have to mess with it and see what I can come up with.

Oh I did figure a sneaky way to run the tracer wire. I used some old heavy string trimmer line and ran down from the bottom spare tire mount hole into the tank area, then the other end and ran up from the same hole to the hea d set. That stuff is heavy enough to snake through but it doesn't kink when the "loop" pulls through the mounting hole.

I haven't had that trimmer for years...And my wife wonders why I never throw anything away!

Patrick,

In your web report you say:
[quote] A final note about CHT is that when you roll off the throttle the CHT tends to go up before it comes down. It!s not uncommon for two strokes to seize when rolling off the throttle after a hard run. This is due to running too close to the thermal limits of the oil and then reducing the lubrication. It!s a tricky situation when you know that holding WOT will push you over the limit AND rolling off it likely to as well. [unquote]

Were you talking about earlier 2T engines?
Years ago, my SS180 seized at 12400 miles while running on the flat at 50mph with mid-throttle and on a cool night. A points failure caused a second soft seize at 48200 miles in much the same conditions. I never had any trouble going down long hills after climbing them. Plug chops always looked OK if not a little rich. Surely timing must have been involved in both cases. Our premix oil at the time was ordinary 30-40 SAE mineral engine oil.

I thought that in later engines, the oil pump delivering in relation to rpm rather than throttle opening only, modern synthetic oils, and electronic ignition were supposed to have eliminated this problem.
Still, monitoring temperatures is a great idea.

Ken.

well it arrived and it is installed. I do need to build up the diameter of the mirror stem some more but I'm very happy with the location.

I went for a ride and I was running at about 300 deg F. I figure I need to find my "normal" range.

There has been lots of gauge threads lately and often the conversation shifts to "CHT or EGT", or "CHT vs EGT". I'd like to make a case for "CHT and EGT".

When we have both on one analog gauge we see something that we don't get any other way. I've tried to illustrate this in the attached graph. The place where the CHT hits a maximum is at lower RPM, while the EGT goes up really quickly above some RPM. With proper jetting the temps will be under their respective limits across the whole power band.

Consider the following events and how the temps would change:

We are accelerating on level ground. In first gear we pass through the point of high CHT so fast that it doesn't have time to rise much if any. We rev out till power is falling off and the EGT starts to go above the limit, then shift to second. As we accelerate through 2-4th we don't see much happening in the CHT but as we reach the top of the rev range in each gear the EGT goes up to the limit.

Now we are flying along at top speed on level ground and our jetting is perfect to keep the EGT right at the limit. we could do this all day and never get into trouble, it's a happy place to be.

The road starts to climb and gradually gets steeper and steeper. As the bike slows heading up the grade we see that the EGT is under the limit but the CHT keeps rising as the bike slows. As the CHT goes above the limit we decide to down shift and see that the CHT falls back to acceptable limits.

We crest the hill in 3rd, shift into 4th and accelerate back up to our top speed.

Now the road starts to descend and we tuck in to see what we can do with a bit of help from gravity. As we accelerate down the hill we see that the EGT is quickly rising above the limit. We decide to back off and leave blowing up the bike for another day.

That's a good study there oops.. the dual gauge looks like it really does offer a good meshed comparison of what's going on... Good stuff.. has me thinking.
It's a good illustration of what your motor goes through when you're not riding on the flat streets.. it's really being pushed much more than we might realize w/o the gauge.. and a CHT only tells 1/2 the story!!!!.. really valuable tools gauges are... they may actually take away a bit of the "free-wheelin, give it gas and go" factor, but they'll save your ass.. just about the time you think it can't get any funner and sieze.
Thanks for sharing.

Oh I locked one up at about 65 on CBR 2012 with CHT and EGT...but I did know I was pushing the limits...I pushed just a litttttttle bit too hard!

Bringing up an old thread, yes I know, even received a pop up box telling me. This is the thread I read as a newbie two years ago and reason I bought an egt gauge when I started tuning.

Working on tuning my reed setup, and trying to understand two readings. At a cruising speed of 55 - 60mph for a few miles minimum both gauges were at a steady reading. I had a CHT of about 255°F under spark plug, I also have shrink tubing around sensor to reduce air cooling for CHT. EGT was 1300°F. Never had this issue, my thoughts of a 255°CHT is a bit rich, 1300 EGT is a bit lean. Didn't have my AFR meter running.

Maybe advance timing a degree to fire sooner? More heat absorbed in cylinder head less out exhaust as waste? I need to check timing again to see where I'm at. I have a kytronik ignition so I could probably pick out a different curve at 5800 RPM cruising speed to advance timing a bit to see what happens.

https://resources.savvyaviation.com/understanding-cht-and-egt-2/

If I'm dealing with those two indicators, I could error on side of caution and richer up 1/4 throttle needle to lower EGT. But that would lower CHT also.

This is a great thread for a newb like myself. I would never had thought that an engine could seize rolling off the throttle after a hard run. It makes sense considering how a 2 stroke gets its lubrication. I have noticed while watching x-kit top speed videos that riders often rev the engine as they are slowing down. I was wondering if this was to keep up oil flow. Gauges are great but can take away from the enjoyment of riding at least for some.

Gauges are great tools for tuning. After that hopefully setup is robust enough to not have to watch them constantly.

That's the plan. Once you get to know and trust the machine it becomes the occasional glance.