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Discussion Starter #1 (Edited)
Howdy from rural Arizona. Just bought out first ATV, a very used 1988 TRX300 (2wd).
It had a broken axle, came with a new replacement. Got the axle in but some parts were missing. The nuts and lock nuts on either side of the diff/brake, hub nuts, lug nuts etc. Have replacements coming from Bike Bandit.
Engine turns but haven't started it yet. I'll address that once it's back on the ground.
Paid $500 for it so it will make for a interesting project.
Hoping to find helpful info on this forum.

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Discussion Starter #3
All the axle parts arrived, well, need 6 more lug nuts.
So it's on the ground on its wheels.

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Discussion Starter #4
Engine cranks. Carb getting fuel (and I have starting fluid).
What I'm missing is spark. Old plug was fouled, new plug no spark. Connections to coil and cdi look good.
So new coil and cdi box on order.
I did also clean the left handlebar switch.

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Do you have 12 volts on both the black wire and the black wire with the white stripe at the CDI unit when the key and handlebar switch are in the on or run position?
 

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Discussion Starter #6
Won't be home until next week to work on the TRX (I'm a truck driver).
But I had an idea (oh no. No no nonono).
I have two Yamaha XS1100 at home that run quite well. They are shaft-drive...

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Discussion Starter #7
Do you have 12 volts on both the black wire and the black wire with the white stripe at the CDI unit when the key and handlebar switch are in the on or run position?
My 1988 TRX300 has only blue & pink, then black & red & red/brown.
No black/white.
I have battery voltage to the black with the key on. Stop/run doesn't matter.
And still no spark with new CDI and coil.

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Sorry - my error - I was looking at a 98

You have 6 wires on the CDI unit - there is another box that looks like a CDI, but it is the alarm unit - the alarm unit has 5 wires, brown with a red stripe, black, dark green, pink and blue with a red stripe - the CDI has black with a yellow stripe, dark green (ground), blue with a yellow stripe, yellow with a white stripe, blue with a white stripe and green with a red stripe.

The black wire is hot when the key switch is on - it goes from the key switch to various places, but we are only concerned with ignition at this time - the black wire goes to the handlebar engine stop switch - when that switch is on, the black/white wire is hot - the b/w wire plugs into blue/wht wire that goes to the CDI box - do you have 12 volts on the blue/white wire? And does the dark green wire have continuity to ground?

Beyond this you will need a peak voltage tester to test the output of the pulse generator, the output voltage to the coil and the voltage to the spark plug.

Without a peak voltage tester, check the continuity of the pulse generator and the ignition coil - go through the connections cleaning and lubricating them with dielectric grease - check the continuity of the spark plug cap and always test using a new spark plug - be sure to verify good grounds at all points requiring ground - don't concern yourself with the alarm unit - it's only function is to turn the oil temperature light - the ignition will work without it.

Let me know where this get's you
 

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Discussion Starter #9
It fires up, with starting fluid.
Very little fuel in the tank. Only flows on reserve.
I'll get more gas when we go into town.
Otherwise it's carb time.

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Discussion Starter #10
FWIW, I do have experience with older vehicles.
Current motorcycles are a 1978 & 1980 Yamaha XS1100.
My transportation to/from work is a 1968 F100.
Work truck is a 2020 Volvo VNL670

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Discussion Starter #11
Got it running. Not running very well, but running.
The fuel inlet to the carb was plugged, so no fuel. Rest of the inside of the carb looked ok, no varnish.
It bogs and dies at mid RPM.
The slide vacuum diaphragm is iffy and the Alaska plunger thing on the bowl is kaput. I might just get a carb and petcock off Amazon or Ebay (any suggestions on a good one, or one to avoid?).
Rode it around the yard (several flat open acres of desert).
Now we need a few more. I think a quad and/or dirt bike each (4 of us) and a 4 person side by side.

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Discussion Starter #13 (Edited)
Best suggestion is to rebuild the original carb unless it's beyond repair
I think the problem is the slide diagram. Replacement for that is $60. A Chinese knock-off of the Japanese carb is $30.
Might get the knock-off and use that diaphragm in the old carb.
Other than the 2 parts mentioned, the carb was in really good condition. All the jets and passages were clear (other than the fuel inlet).
One thing that I'm glad of, it has only 1 carb. I'm used to dealing with 4 at a time.

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What makes you think the slide in a Chinese cheapo carb will be the same weight and dimension as the Keihin carb?

That means I can take parts from an AFB parts in a Carter carburetor or get a fuel injector for a Volkswagen diesel to put in a Caterpillar bulldozer.

Either fix the OEM carb or install a cheap piece of junk purchased from Ebay!

And the statement that "I think the problem is the slide diagram." What makes you think it's the slide? If the diaphragm is not perforated or torn, then it is not the problem.

Send me the carb and I will tell you what's wrong with it. Better than that, I'll fix it for the cost of parts and postage. I can get a new slide from Honda for $45.
 

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Discussion Starter #15
More replacement of missing parts arriving Mon & Tue.
Hope to get it running more consistently.

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Discussion Starter #16
Installed the airbox cover and seal, they were missing. This didn't help the way it was running (but it doesn't hurt either).
The exhaust heat shield arrived this morning. Purely a comfort item.
This afternoon got the new petcock and carb kit.
Installed the new petcock. The old one leaked and the screen was nonexistent, mostly. The base of it was corroded to the tank outlet. It appears someone poked out (in?) the mesh.
It now runs much more consistently once well warmed up. Previously it would not rev to higher rpm, or it would bog at low rpm but run good n fast. Now it does both.
I may still install the carb kit, mostly for the new float needle/seat. The carb was varnish-free despite the fuel inlet initially bring clogged.
Getting closer to trusting it enough to ride it somewhere other than our flat average. Live in rural AZ next to a few rugged mountain ranges, like just a few miles away on each side of our valley.
Once running right, it will need front wheel bearings and the left rear tire has a slow leak (2-3 day leak).
New rear axle spins by hand and has no play. Lock nuts still tight (I marked them).

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