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02 Sep 2019
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TOPIC: Dt175 76 blowing bulbs and now no spark

Dt175 76 blowing bulbs and now no spark 23 Jun 2019 06:50 #11

  • MarkT
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That's the rectifier... just a diode to convert voltage from stator from AC to DC to charge the battery. It only allows the "+" of the AC voltage through.

Voltage before rectifier:


Voltage after rectifier:


OEM Yamaha rectifier usually has male and female terminals on the diode (rectifier) so you can't hook it up backwards (which would let only the "-" through to the "+" side of the battery). Yours looks like it has the same wiring connector on both terminals. You'll need to make sure yours is connected properly.

Regulator is a small box with a single yellow wire going into it. 1976 was the first year Yamaha added one at the factory. With a working Yamaha regulator, it's extremely rare to blow a bulb. Did you check your VIN to verify it's a 1976? From memory the VIN number started with "559" in 1976. There are VIN tables in the Tech Library.

Spark plug looks oil and/or fuel fouled, not lean. If bike has been sitting a long time and hasn't been warmed up and ridden under load and higher rpm a good distance it might be "normal"...
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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

Dt175 76 blowing bulbs and now no spark 23 Jun 2019 07:08 #12

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Ok thanks for the knowledge
Plug was new in 3 days ago
It has always struggled with idle, any choke and it dies
With the new plug it ran as sould and I could adjust the idle correctly but am thinking now it may be the oil pump fouling the plug,did have an issue after 10mins of riding it lost power and wouldn't rev out, quickly removing the oil feed brought it back to life, haven't seen a regulator anywhere on bike including below air filter but will check the vin and tech docs, might have to consider removing the pump and running pre mix see if it helps..once I get it started that is

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Dt175 76 blowing bulbs and now no spark 23 Jun 2019 07:36 #13

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https://www.partzilla.com/catalog/yamaha/motorcycle/1976/dt175c/electrical

according to this there is a regulator somewhere at the front of the frame so will have another dig when it stops raining..
looks like mine is a DT175C

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Dt175 76 blowing bulbs and now no spark 23 Jun 2019 11:21 #14

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1976 DT 175 voltage regulator.
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It's better to remain silent and be considered a fool than to speak and remove all doubt.

Dt175 76 blowing bulbs and now no spark 23 Jun 2019 11:27 #15

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My DT175C runs rich too and fouls plugs. My son in law rode it the other day and forgot to push in choke and fouled the plug so bad I got no spark. I put a new plug in and it fired right up. Before removing oil pump, make sure it’s set up right by insuring the marks are aligned when the throttle is closed. Also, eliminate the possibility it’s pulling in crank case oil through the seal. Drain your crank oil thoroughly and add exactly 650ccs. Ride the heck out of the bike with a new plug or two with you. Put some distance on it if you can. Drain crank again and measure how much oil came back out. That will give you an idea if it’s burning crank oil to foil the plugs.

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Dt175 76 blowing bulbs and now no spark 23 Jun 2019 13:45 #16

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Ok thanks, nice bike
Curious but I have looked and I cannot see a regulator anywhere on the bike
Will try a new pulg tomorrow and then should know if its an oil fouling issue which then would point to crank seal or over enthusiastic oil pump?

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Dt175 76 blowing bulbs and now no spark 23 Jun 2019 15:53 #17

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MidlifeMotor posted a nice picture of the 1976 regulator located on the air cleaner box right behind the carb just behind the kickstarter.

(It was my 1975 that someone added one under the front of the gas tank, sorry)

On a 1976 or any model that came from the factory with a regulator, you MUST have a regulator or the bulbs will continue to burn out immediately. (Yamaha boosted the power from the stator on the regulator models)

Here's a pic of my 1976 regulator... same place as Midlife's... Some later regulators have more of a "finned" case and even later, they got smaller. All have the same two-bolt mounting and a single yellow wire coming out and a ground wire to the case at one of the mounting bolts. If you don't have one, you'll need to get one.



And again, if the bike has been sitting the BEST thing you can do is ride it hard for a while. Most likely it's simply loaded up. Starting it in the garage and letting it idle with a little bit of revving is not going to clear it out. It needs to be ridden.

Checking the oil pump cable adjustment as suggested is also a good idea. Disconnecting the pump is not a good idea. I've run the pump and premix both and not fouled a plug. Yamaha even recommended the pump AND 32:1 premix on MX models used for racing. They wouldn't do that if it would foul plugs.

More likely the fouling is due to fuel richness. Air filter foam not flowing air properly due to age, incorrect installation, or over-oiling is the most likely reason.

P.S. I run my old 32:1 premix in modern four stroke lawn equipment that's CARB emissions legal... No visible smoke at all and plug looks new. They run those engines very lean which makes the difference.
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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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Dt175 76 blowing bulbs and now no spark 23 Jun 2019 23:05 #18

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By the way that’s Utah red and tan dust on the bike in the pic, NOT rust haha.

Mark T you may have helped me solve a problem on my 76 DT175 running rich. Gonna check the air cleaner as you suggested above.

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Dt175 76 blowing bulbs and now no spark 24 Jun 2019 01:46 #19

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hi weird as i have been running this bike for a while now and didn't start blowing bulbs till recently... also i note the full beam light on instrument panel is increasing in brightness when revved
no regulator that i can see and has always been that way in my ownership, might this be an earlier model that prev though without regulator?
or its been rewired and the prev owner ran daytime only?
seems like a wild idea but as i say in my ownership it has been good with bulbs for at least a year of running..
air filter i will clean again, have just obtained a air filter cage which it didn't have before so at least it sits right in the box now..
it did have a intermittent issue where it would lose power and not rev out, quickly removing the oiling pipe brought it back to life
will investigate the oil pump settings too
will get a new plug in later and update, if it is fouled plug then i will do the cranks seals anyways
thanks again
D

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Dt175 76 blowing bulbs and now no spark 24 Jun 2019 04:17 #20

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ok so new plug and whomp it started first kick and is idling perfectly, loads of grunt etc
so definitely fouled plug but as plug was new a few days earlier i kind of discounted that as being a potential issue..
checked transmission oil and still at level always has been so no cranks seal issues
i noted plug was a BR8ES rather than a B8ES
still no sign of a regulator though
D

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